The relevance of delivery mode and other programme ...

International Journal of Behavioral Development# 2005 The International Society for the2005, 29 (1), 35–47 Study of Behavioural Developmenthttp://www.tandf.co.uk/journals/pp/01650244.html DOI: 10.1080/01650250444000315The relevance of delivery mode and other programmecharacteristics for the effectiveness of early childhoodinterventionHenk Blok, Ruben G. Fukkink, Eveline C. Gebhardt, and Paul P. M. LesemanUniversity of Amsterdam, The NetherlandsAlthough it is generally believed that early intervention programmes are an effective means tostimulate children’s cognitive development, many questions remain concerning programme designand delivery. This article reviews 19 studies into the effectiveness of early intervention programmespublished from 1985 onward. The database comprised 85 different outcomes or effect sizes (71 inthe cognitive domain, 14 in the socioemotional domain). The overall effect size estimate was d ¼0.32 (SE ¼ 0.05) in the cognitive domain, and d ¼ 0.05 (SE ¼ 0.02) in the socioemotionaldomain. Effect sizes were found to depend on delivery mode. Centre-based interventions andinterventions following the combined home- and centre-based delivery mode produced greater effectsizes than did home-based programmes in the cognitive domain, but not in the socioemotionaldomain. The programme inclusion of coaching of parenting skills was also positively related tooutcomes in the cognitive domain. Several other programme characteristics, including age of onset,programme length and intensity, continuation after kindergarten, and the inclusion of social oreconomic support, appeared not to be uniquely related to outcomes.IntroductionIt is generally believed that early intervention enhances theopportunities of children who are socioeconomically orculturally disadvantaged. Many independent studies havecontributed to the belief that early intervention is effective.The comprehensive reviews carried out by Lazar andDarlington (1982) and McKey, Condelli, Ganson, Barrett,McConkey, and Plantz (1985) marked the end of years ofdispute over the effectiveness of early intervention fordisadvantaged children. Since then, the perspective on earlyintervention has broadened. More comprehensive approacheshave been advocated, encouraging a combination of differentservice delivery formats, the inclusion of additional parentcomponents, and the longer duration of programmes, bystarting them at an early age and continuing them afterkindergarten. More specifically, four related issues pertain tothe required comprehensiveness of early intervention toachieve long-term effects on the development of disadvantagedchildren.First, there has been a growing awareness in the field thateffective programmes should target both the child and theparents to promote stable effects on the child’s development.Some programmes have combined a child-focused, centrebasedapproach with a parent-focused, home-based approachto reach this goal, while others have adopted either a specifichome-based or a specific centre-based approach. The secondissue, which is related to the first, is the question which parentfocusedcomponents yield additional benefits for the developmentof children. Some programmes include a component thatis focused on parenting skills, whereas others offer the parentssocial and economic support. The third issue concerns thetiming: When should a programme begin, and when should itend? These three issues, all of which pertain to the requiredcomprehensiveness of early intervention programmes, havebeen specifically linked in recent discussions to the effects ofearly intervention in the long term—which is the fourth andfinal issue. Furthermore, although the interest in cognitivegains from early intervention has not diminished, it is nowcomplemented with the study of socioemotional outcomes. Wediscuss these four themes below in the context of theconceptual framework developed by Ramey and Ramey(1998) as a way of introducing our research questions. Thisframework—which is called biosocial developmental contextualism—derivesfrom social ecology, developmental systemstheory, and developmental neurobiology, and addresses theprinciples of effective early intervention.Delivery format of programmesBiosocial developmental contextualism clarifies that there aremultiple pathways in early intervention to improve children’sdevelopment. Programmes may influence the parents orprovide direct educational experiences to children, or theymay do both. Three corresponding programme types aredistinguished: home-based, centre-based, and a combinationof home- and centre-based delivery.Correspondence should be sent to Henk Blok, University ofAmsterdam, Faculty of Social and Behavioral Sciences, SCO-Kohnstamm Instituut, Wibautstraat 4, 1091 GM Amsterdam, TheNetherlands; e-mail: H.Blok@uva.nl.This research was supported by a grant from the NetherlandsOrganization for Scientific Research (NWO), contract 490-23-2006.Interested readers may obtain the search profiles (used in ERIC andPsychINFO) and the complete data matrix from the first author.

36 BLOK ET AL. / EFFECTIVENESS OF EARLY CHILDHOOD EDUCATIONHome-based interventions rely on an indirect way ofstimulating children’s development (e.g., through parenttraining). A common starting point of home-based programmesis the belief that the parents of disadvantagedchildren use less effective parenting strategies because theylack the necessary knowledge (Goodson, Layer, StPierre,Bernstein, & Lopez, 2000). It is hypothesised that home-basedprogrammes lead to a change in parental attitudes, behaviour,and school involvement. This results in more and higherqualityparent–child transactions and family-orchestrated childexperiences (Guralnick, 1998), and these have positive effectson the child. However, reviews of the available evidence for theeffects of home-based programmes are not too optimistic(Gomby, Culross, & Behrman, 1999). Parenting interventionalone is viewed as too weak, because parenting beliefs andpractices cannot be altered easily (Halpern, 2000). Otherauthors have concluded that although home-based programmescan affect parental attitudes and behaviour, suchprogrammes do not result in positive child outcomes (Farran,2000).Centre-based programmes provide children with directeducational experiences, for instance in a daycare or preschoolsetting. Findings in this field have shown that significant effectscan be achieved for developmental competence and achievementtests at the end of preschool and into kindergarten. Thereis growing evidence that direct provision in centre-basedapproaches is more effective than indirect provision in homebasedapproaches (Barnett, 1995; Bowerman, Donovan, &Burns, 2001; Farran, 2000; McGuire & Earls, 1991; Ramey &Ramey, 1998). Ramey and Ramey clearly favour a centrebasedapproach, as they are convinced that the direct provisionof learning experiences leads to larger and more enduringbenefits than does indirect provision (e.g., parent training).Several programmes offer a combination of home-based andcentre-based components. Combining the two delivery formatsmay create more pathways for positive change in families’ livesand have synergetic effects (Smith & Zaslow, 1995). Surprisingly,however, the seemingly widely shared preference for acombined approach is not unequivocally supported by reviews.While in their narrative reviews Barnett (1995) and Farran(2000) favour a combined approach, White, Taylor, and Moss(1992) found no convincing evidence that the involvement ofparents results in more effective outcomes. White et al.reviewed eight studies of disadvantaged children in which thedegree of parental involvement represents the only differencebetween the experimental groups. The average effect size for allstudies across all child measures was 0.11 of a standarddeviation, with the best designed studies arriving at the weakestresults. To conclude, there are still unanswered questionsconcerning the effectiveness of these service delivery models, asnoted by Campbell and Ramey (1995, p. 745).Programme comprehensivenessBiosocial developmental contextualism promotes a moreinclusive view of early intervention (Ramey & Ramey, 1998).The field of early intervention has moved on from a specificfocus on the deficits of the child to, in more recentprogrammes, a focus on both child and family. Many of theseprogrammes include a component that focuses on the coachingof parenting skills. Other programmes also offer the parentssocial and economic support. The promotion of childdevelopment, the enhancement of parenting skills, and theprovision of adult services can also be combined in a threeprongedapproach.A principal issue is which goals deserve primary attention inearly intervention. Reynolds (1998), for example, argues that‘‘although there is consensus about the importance ofproviding comprehensive services, there is less consensusabout the relative importance of these services and the extentto which these services should be provided’’ (p. 508). Forexample, it can be hypothesised that the coaching of parentingskills, which can be conceived as an indirect but targetedapproach to stimulate the development of children, is morebeneficial to children than adult economic or social support,which is primarily focused on the parents. Furthermore, it is anopen question whether interventions that are theoreticallypowerful are also more effective in practice (Gomby, Larner,Stevenson, Lewit, & Behrman, 1995).Timing and duration of programmesResearch in developmental neurobiology has recently underlinedthe importance of very early stimulation. It is becomingincreasingly clear that neurodevelopment is for a large partexperience-driven, and that brain development depends onearly experiences (Shore, 1997). This motivates an early startof interventions that aim at the improved development ofdisadvantaged children.Halpern (2000) has stressed that intervention should notonly start early, but also be continuous in order to be effectivein the long run. Farran (2000) and Rimm-Kaufman and Pianta(2000) specifically emphasised the importance of the transitionfrom kindergarten to primary school, which evokes the need forcontinued support. According to Reynolds (1998), earlyintervention should be continued into second or third gradein order to promote long-term effectiveness.Retention of effectsThe above-mentioned issues of multiple combined formats,the inclusion of additional components, and the timing andduration of programmes have been specifically discussed in thecontext of the long-term effectiveness of early intervention(Barnett, 1995; Gomby et al., 1995; Reynolds, 1998).Basically, there are two hypotheses concerning the outcomeof early intervention. The first predicts that the immediateeffects are sustained. The cognitive advantage hypothesis, forinstance, predicts that early intervention ‘‘initiates a positivecycle of scholastic development and commitment that culminatesin improved developmental outcomes in adolescence andbeyond’’ (Reynolds, Mavrogenes, Bezruczko & Hagemann,1996, p. 1119). However, the second, rival hypothesis predictsthat effects fade over time. Farran (2000), for example,emphasised that most programmes focus on concrete skillsrelated to readiness tests, whereas profound curricular changestake place in third and fourth grade. Several evaluations haveindeed shown a fading of the positive results (Blok & Leseman,1996; McKey et al., 1985). Significant effects of centre-basedprogrammes, for example, are rare by—and nonexistentbeyond—first grade, according to Farran (2000) and Gilliamand Zigler (2000). The increasing number of studies and thelonger span of follow-up studies enable not only a moreprecise, but also a more general estimate of the retention ofprogramme effects in the long run.

INTERNATIONAL JOURNAL OF BEHAVIORAL DEVELOPMENT, 2005, 29 (1), 35–47 37Goal of the studyThe goal of the study was to answer questions regarding thedelivery and design of early intervention programmes fordisadvantaged children. The inclusion of additional programmecomponents, and the timing, duration, and intensityof programmes were among the design features. We also paidattention to the recency of programmes. Finally, we distinguishedbetween the immediate effects of the programme andtheir retention. Effectiveness is defined at the child level,distinguishing between cognitive and socioemotional effects.To answer these questions, we conducted a meta-analysis ofthe outcomes published from 1985 onward. We decided torestrict ourselves to this year of publication because manyearlier results had already been reviewed (in, e.g., Lazar &Darlington, 1982; McKey et al., 1985; White et al., 1992).MethodSelecting the studiesWe searched ERIC and PsychINFO—the major databases inthe fields of education and child development—combiningthree groups of descriptors: one to indicate the independentvariables (e.g., programme evaluation, curriculum evaluation,course evaluation, home programmes, parent training, daycare),one to indicate the dependent variables (e.g., outcomesof education, basic skills, academic achievement, cognitivedevelopment), and one to indicate the age of the students (e.g.,early childhood education, preschool education, kindergarten,toddler). We thus focused explicitly on programmes with aneducational orientation, excluding programmes oriented solelytoward socioemotional development or child health. We alsoexcluded studies of gifted children and of children who are atrisk for medical reasons (e.g., premature birth, handicapped,impaired, retarded, disabled). All selected studies appeared tofocus on disadvantaged children.The references of collected papers and articles weresearched for additional references. Additionally, relevantstudies were suggested by experts. We deliberately restrictedour search to articles published in peer-reviewed journals. Therationale was that limiting studies to those passing the test ofpeer review minimises the risk of admitting studies of poorquality. For the same reason, studies had to include anontreated control group in order to qualify for our analysis.Our final set comprised 19 studies, which were subsequentlysubjected to the review procedure.Deciding on the relevant comparisonsThere was not always a simple one-to-one correspondencebetween studies and experimental comparisons, namelycomparisons between an experimental and a control group.Some studies reported the effects of more than one experimentalcondition, while others evaluated essentially the sameexperimental condition in more than one sample. On the otherhand, one and the same experimental comparison wasdifferentially conceived of in different publications, for instancewhen one article reported on the full sample, and a subsequentarticle—evaluating follow-up results—reported on only asubsample of the original sample. We therefore decided toadopt the level of the experimental comparison as the unit ofcoding.Relatively straightforward decisions could be taken forseveral studies, whereas decisions were more complicated inthe case of others. Kagitcibasi, Sunar, and Bekman (2001)reported effects of the Turkish Early Enrichment Project—anadaptation of the Hippy (Home Instruction Program forPreschool Youngsters) programme, which was originallydeveloped in Israel (Lombard, 1981). They complemented itwith a mother training component. Their study was a 3 2 2 factorial design with three categories of early childhood care(preschool, daycare, homecare), two levels of home intervention(Hippy, no Hippy), and two age levels (3 and 5 years atthe beginning of the study). Because the number of students inthe different cells was rather low, we decided to aggregate thedata by age levels. Furthermore, we considered the Hippy/noHippy factor as our main factor of interest. Accordingly, thestudy allowed us to make three comparisons, namely the effectof Hippy/no Hippy in three early childhood care arrangements:preschool, daycare, and homecare.The results of generic Head Start programmes have beenreported by Lee, Brooks-Gunn, and Schnur (1988) and Lee,Brooks-Gunn, Schnur, and Liaw (1990). In both articles,participation in Head Start was compared to either nopreschool or other preschool experiences, allowing twocomparisons (Head Start vs. no preschool, and Head Startvs. other preschool). The first article provided data frompretests and posttests, the latter administered immediatelyafter the end of the intervention. The second article reportedno pretest results, but only posttests results 1 and 2 years afterthe end of the Head Start intervention. Although the samplesoverlapped considerably, they were not identical: The sampledealt with in the follow-up article was 33% smaller (the HeadStart group had shrunk from 414 to 333, the no-preschoolgroup from 390 to 204, and the other preschool group from165 to 109), excluding all non-black children. We decided tocombine the results of both articles, noting that the results ofthe follow-up measures might be biased.Madden, Slavin, Karweit, Dolan, and Wasik (1993) andSlavin, Madden, Karweit, Livermon, and Dolan (1990)reported outcomes of Success for All (SFA), an interventionprogramme starting in preschool and continuing into Grade 3.Slavin et al. described the first year of SFA (1987/1988), andreported outcomes for five samples (preschool, kindergarten,Grade 1, Grade 2, Grade 3). Only the first two samples wererelevant to our review, as the other samples had received noearly intervention. The results reported in Madden et al.concerned outcomes from the third year of SFA (1990/1991),by which time the programme was running in five differentschools. Some of these outcomes (collected at the Abbottstonschool) were regarded as follow-up results for the students inthe 1987/1988 sample. Other outcomes reflected independentdata gathered from other schools. We extracted four comparisonsfrom the two articles: two concerning Abbottston data(including follow-up results in 1990/1991) and two reflectingGrade 1 (evaluating the effect of preschool and kindergartenintervention, aggregated by school) and Grade 2 (evaluatingthe effect of kindergarten only, also aggregated by school, butexcluding Abbottston), respectively. These comparisons weredefined in this way to avoid an overlap in the sample ofstudents.The outcomes of the Abecedarian project have beenreported in many journal articles, beginning with Burchinal,Lee and Ramey (1989). The research design changed in thecourse of the project, and finally consisted of three experi-

38 BLOK ET AL. / EFFECTIVENESS OF EARLY CHILDHOOD EDUCATIONmental conditions and one control condition. Two experimentalcomparisons were within the domain of our researchquestion. One was that between the CC (control condition,i.e., no preschool, no follow-up programme) and the EEcondition, in which students received preschool education forthe first 5 years of their life, followed by a supplementaryEducational Support Program from kindergarten through 2ndgrade. The second comparison we extracted from the availabledata was that between the CC condition and the EC condition,in which students received only the preschool programme andnot the follow-up programme. The data we used came fromRamey, Campbell, Burchinal, Skinner, Gardner, and Ramey(2000), who presented IQ data from 5 to 15 years old, andschool performance data from 8 to 15 years old.The results of the Chicago Child-Parent Center andExpansion Program (CPC&EP) have also been widelyrepresented in the research literature. We selected the outcomesreported in Reynolds (1994) as our reference data,because the presented intervention groups were the mostrelevant to our research question. We extracted one experimentalcomparison from these data, namely the full interventiongroup with follow-on (denoted as PS þ KG þ PG-3 byReynolds) with the non-CPC comparison group.We found two studies on the effectiveness of a supplementaryemergent literacy curriculum compared to a standardHead Start programme (Whitehurst, Epstein, Angell, Payne,Crone, & Fishel, 1994; Whitehurst, Zevenbergen, Crone,Schultz, & Velting, 1999). The second study is a replication ofthe first, and includes a follow-up of both the original cohortand the replication cohort. Unfortunately, the outcomes of thetwo studies were not reported independently, as the secondarticle (Whitehurst et al., 1999) combined the results of bothcohorts. This left us no choice but to use the outcomes of thesecond article only, as it concerned the biggest sample andprovided follow-up results. The two Whitehurst et al. studiestherefore resulted in one experimental comparison, namelyHead Start with an emergent literacy add-on contrasted with aHead Start-only condition.After all decisions had been made, there remained 34experimental comparisons.Coding of variablesThe experimental comparisons in the database were coded forseveral characteristics (see Table 1). Variables 1–3 concerndesign characteristics, variables 4–11 concern sample characteristics,and variables 12–17 concern characteristics of theexperimental intervention.Because most experimental comparisons resulted in multipleoutcomes, other variables (variables 18–25) were coded atTable 1Coding scheme for the experimental comparisons, and reliability of codingInter-coderVariable Scale reliability a1. Subject assignment 0. Strictly controlled (randomisation or matching at subject level); 1. no strict control 87(randomisation or matching at group level, post hoc comparison, or no control at all)2. Treatment fidelity 0. High in most respects; 1. unknown 1003. Intervention in control group 0. Standard programme, not under control of experimenter; 1. unknown programme 92or no programme at all4. Nation 0. USA; 1. other than USA 1005. Recency of programmeNumerical (minus 1900).93 b(year implementation started)6. Size of experimental group Number of students 1.00 b7. Size of control group Number of students .99 b8. Mean age of students at onset of study Number of months (before birth coded as 0) .96 b9. Percentage of students from ethnic Percentage.96 bminorities10. Level of education of parents 1. Low; 2. mixed; 9. unknown 8711. Level of income of parents 1. Low; 2. mixed; 9. unknown 9312. Delivery mode 1. Home-based; 2. centre-based; 3. combination of home- and centre-based 9613. Length of programme Number of months (a year equals 10 months, unless otherwise indicated by.99 bexperimenter)14. Intensity of programme Number of hours per week .91 b15. Continuation after K 0. No; 1. yes 10016. Inclusion of social or economical 0. No; 1. yes 85support17. Inclusion of coaching of parenting skills 0. No; 1. yes 8518. Effect size at pretest Numerical 1.00 b19. Standard error of pretest effect size Numerical .94 b20. Domain of the posttest 0. Cognition 1. socioemotional development 9321. Time of measurement of posttest Number of months after intervention ended, coded on a time scale of years 1.00 b22. Type of posttest score 0. Observed score; 1. gain score or score adjusted for covariates 9423. Type of posttest effect size 0. Derived by reviewers; 1. reported by experimenters 10024. Effect size at posttest Numerical 1.00 b25. Standard error of posttest effect size Numerical .94 ba Percentage of classifications agreed upon by the two coders, unless otherwise indicated.b Product–moment correlation between the codes of the two coders.

INTERNATIONAL JOURNAL OF BEHAVIORAL DEVELOPMENT, 2005, 29 (1), 35–47 39the level of effect sizes. Hedges’ unbiased estimate d was usedas an effect size estimate (variables 18 and 24). This statisticuses the within-group standard deviation as a method ofstandardisation. It includes a correction factor to obviate biasresulting from small samples. The standard error of the effectsize (variables 19 and 25) was estimated following Hedges andOlkin (1985, p. 86, Eq. 15). Whenever possible, we usedobserved scores to calculate effect sizes. Several experimenters,however, reported only gain scores or scores adjusted forcovariates, indicated by variable 22 (type of posttest score).Some reported outcomes were inherently negative, forinstance when behaviour ratings referred to negative behaviour.In these cases, outcomes were recoded simply bychanging the sign. This correction procedure was applied tothe studies by Goodson et al. (2000), Johnson and Walker(1987), Scarr and McCartney (1988), and Seitz, Rosenbaum,and Apfel (1985).Two independent coders coded all the studies. Inter-coderreliability was estimated by determining the rate of agreementin the case of a nominal scale, or the product–momentcorrelation in the case of an interval scale. The results arereported in the last column of Table 1. The reliability provedto be satisfactory, ranging between 85 and 100% for nominalvariables, and between .91 and 1.00 for interval variables. Inthe case of divergent codes, final codes were established bymutual agreement, and used in subsequent analyses.Many study designs either did not incorporate a pretest ordid not report sufficient statistics to estimate an effect size thatcaptured the initial differences between conditions at thepretest. We were able to determine pretest effect sizes for only40% of our cases. To prevent an excessive loss of data, wedecided to impute zero scores for missing effect sizes atpretesting. This value is close to the mean value we found forcases, which allowed us to estimate a pretest effect size (meanvalue 0.06 with a corresponding standard error of 0.04).Integration of effectsThe coding phase resulted in a file containing 207 differentoutcomes (171 in the cognitive domain, 36 in the socioemotionaldomain) from the 34 experimental comparisons. Weanalysed the data in two steps. We first aggregated effect sizesto the level of the experimental comparisons. This aggregationwas performed separately for each domain and time ofmeasurement, varying from 0 to 180 months after theintervention ended. This aggregation was conducted byweighted integration, in which the results were weighted ininverse proportion to their standard error (i.e., the greater thestandard error, the smaller the weight). The aggregated effectsizes and the corresponding standard errors were estimatedfollowing Hedges and Olkin (1985, p. 112, Eqs. 8 and 9). Thisaggregation model assumes the results within one study to behomogeneous and to differ from each other only on the basis ofrandom differences between the outcome variables. Thestandard errors of aggregated effect sizes are generally smallerthan the standard errors corresponding to the constituent effectsizes, which seems a fair reward for using more than oneoutcome measure. All calculations on aggregations were doneusing the Meta programme (Schwarzer, 1989). This first stepresulted in 85 different outcomes (71 in the cognitive domain,14 in the socioemotional domain).As a second step, outcomes or effect sizes were integratedinto an overall effect size, separately for each domain. Theintegration was performed according to the random effectsmodel (Hedges & Olkin, 1985). The model we specifiedacknowledges the hierarchical and longitudinal nature of ourdata. The model splits the effect size d ijt for experimentalcomparison j from study i at moment t into two components,namely a true effect size d ijt , and an error component e ijt . Thetrue effect sizes are assumed to vary across measurementmoments t, comparisons j, and studies i. The variance of d ijt isexplained by the regression model:d ijt ¼ g 0 þ g n Z nijt þ u ijt þ v ij þ w i (1)where g 0 is the grand mean, Z nijt are characteristics of thestudies (n being the index referring to the characteristics),comparisons and measurement moments, and u ijt ,v ij , and w iare residual error terms at the three levels distinguished. Themodel makes it possible to distinguish between three variancecomponents, viz. s 2u (the variance between measurementmoments t), s 2 v (the variance between experimental comparisonsj ), and s 2 w (the variance between studies i ). The modelalso enables testing whether any of the parameter variances aresignificantly different from zero with the test statistic Q. Ifstudy outcomes are heterogeneous, it is worthwhile trying torelate the heterogeneity to the various characteristics Z nijt .Ifnot, the study outcomes are homogeneous and no explanatoryvariables need to be introduced in equation (1). Thespecification and testing of models was carried out withMLwiN, using restricted maximum likelihood estimation(Goldstein et al., 1998; Hox, 2002). Analyses were performedseparately for both domains (cognition, socioemotional development).ResultsDescription of the studies in the databaseThis subsection briefly describes the studies in our database,which yielded 34 different comparisons (Table 2).Assignment of the subjects to the different conditions of thecomparison proceeded according to strict guidelines (atrandom, by matching, or by blocking) in only 16 cases. Inother cases, less strict procedures were followed (e.g., randomassignment or matching of intact groups), or assignment wasnot under the control of the investigator.Treatment fidelity was reported to be high in all or mostrespects for 11 of the 34 comparisons. For the othercomparisons, no information could be found. However, thisdoes not necessarily mean that the treatment was jeopardised.We found the same lack of information with respect to thecontrol condition. Students in the control condition mostlyfollowed a ‘‘standard programme’’.The sample size was generally small, averaging 77 for boththe experimental and the control conditions. This averageexcludes the outlying large sample size of the study byGoodson et al. (2000), which featured about 1600 childrenin both conditions. The experimental group contained morethan 100 students in only 8 of the 34 comparisons. Evidently,such small sample sizes imply generally low power to detect adifference in outcomes. Most students belonged to an ethnicminority group (average: 81%, taking experimental and controlgroups together). Median student age at the start of theintervention programme showed considerable variation, rangingfrom pre-birth to 64 months (average 37 months). Boththe socioeconomic status and the income of parents were

40 BLOK ET AL. / EFFECTIVENESS OF EARLY CHILDHOOD EDUCATIONTable 2Summary of characteristics of the studies in the meta-analysisVariablesReferences Experimental comparisons 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17Baker et al., 1998. Cohort I (Hippy vs. Control) 0 0 1 0 90 37 32 58 80 1 1 1 14 2 0 0 1Cohort II (Hippy vs. Control) 0 0 1 0 91 47 66 54 75 1 1 1 20 2 0 0 1Gersten et al., 1988. Direct instruction (K-3) vs.1 1 0 0 70 54 121 64 83 9 1 2 40 9 1 0 1ComparisonGoodson et al., 2000. Comprehensive Child Development 0 0 0 0 90 1640 1560 18 74 1 1 1 33 1 0 1 1Program vs. ControlHowell et al., 1990. Peabody LDK-R vs. Control 1 1 0 0 88 19 19 55 98 1 1 2 6 4 0 0 0Boehm RG vs. Control 1 1 0 0 88 19 19 55 98 1 1 2 6 4 0 0 0Bracken CDP vs. Control 1 1 0 0 88 19 19 55 98 1 1 2 6 4 0 0 0Johnson & Walker, 1987, Houston Parent–Child Development 0 1 1 0 75 51 88 12 100 1 1 3 20 7 0 0 11991; Walker & Johnson,1988.Program vs. ControlKagitcibasi et al., 2001. Education daycare (ED) with mother 0 0 0 1 85 27 37 48 0 1 1 1 14 2 0 0 1training (MT) vs. ED without MTCustodial daycare (CD) with mother 0 0 0 1 85 40 65 48 0 1 1 1 14 2 0 0 1training (MT) vs. CD without MTHome care (HC) with (MT) vs. HC 0 0 1 1 85 23 63 48 0 1 1 1 14 2 0 0 1without MTLee et al., 1988; 1990. Head Start vs. No preschool 1 1 1 0 69 333 204 50 100 1 1 2 9 20 0 0 0Head Start vs. Other preschool 1 1 0 0 69 333 109 50 100 1 1 2 9 20 0 0 0Olds et al., 1994; Treatment 3 vs. Treatment (1 þ 2) 0 0 1 0 77 78 148 0 0 1 1 1 4 1 0 0 1Olds et al., 1998. Treatment 4 vs. Treatment (1 þ 2) 0 0 1 0 77 88 148 0 0 1 1 1 24 1 0 0 1Slavin et al., 1990;Success for All (SFA) preschool0 1 0 0 87 40 40 49 90 9 1 2 10 15 1 0 1Madden et al., 1993. 1987/1988 vs ControlSFA kindergarten 1987/1988 vs. Control 0 1 0 0 87 60 60 60 90 9 1 2 10 25 1 0 1SFA grade 1 1990/1991 vs. Control 0 1 0 0 90 246 246 49 99 9 1 2 30 12 0 0 1SFA grade 2 1990/1991 vs. Control 0 1 0 0 90 185 185 49 99 9 1 2 30 12 0 0 1Ramey et al., 2000.Abecedarian (preschool þ K-2 transition) 0 1 0 0 72 25 22 4 98 1 1 3 96 13 1 1 1vs. ControlAbecedarian (preschool only) vs. Control 0 1 0 0 72 22 22 4 98 1 1 3 50 20 0 1 1Reynolds, 1994.Chicago CPC and EP (full intervention) 1 0 0 0 72 160 191 42 100 9 1 2 50 15 1 0 1vs. Non-CPC comparison groupRiksen-Walraven et al., 1996. Instapje vs. Control 1 0 1 1 94 37 38 13 100 1 1 1 4 2 0 0 1Scarr & McCartney, 1988. Mother Child Home Program vs. Control 0 0 0 1 78 78 39 27 60 2 2 1 20 2 0 0 1Schweinhart, 2000;Perry Preschool vs. Control 0 0 1 0 62 58 65 36 100 1 1 3 15 14 0 0 1Luster & McAdoo, 1996.Schweinhart et al., 1986. Distar vs. Control 1 1 1 0 67 23 65 36 93 1 1 3 20 13 0 0 1High/Scope vs. Control 1 1 1 0 67 22 65 36 95 1 1 3 20 13 0 0 1Nursery vs. Control 1 1 1 0 67 23 65 36 93 1 1 3 20 13 0 0 1Seitz et al., 1985. Family Support Intervention vs. Control 1 1 1 0 68 18 18 0 83 1 1 3 30 9 0 1 1Tuijl et al., 2001. Hippy vs. Control (Moroccan sample) 1 0 0 1 96 83 55 57 100 1 1 1 15 2 0 0 1Hippy vs. Control (Turkish sample) 1 0 0 1 96 122 59 57 100 1 1 1 15 2 0 0 1Wasik et al., 1990. Care þ Family Education vs. Control 0 1 0 0 78 14 22 2 90 1 1 3 48 25 0 1 1Family Education vs. Control 0 1 0 0 78 25 22 2 90 1 1 1 48 2 0 1 1Whitehurst et al., 1999. Head Start þ Emergent LiteracyIntervention vs. Head Start1 1 0 0 92 140 140 36 67 2 1 3 7 3 0 0 1See Table 1 for explanation of variables and codes.generally low. On average, 76 and 97%, respectively, of theparents were classified in the lowest category. Of the 34comparisons, 26 were conducted in the United States, 3 in theNetherlands, 3 in Turkey, and 2 in Bermuda.The comparisons were more or less uniformly distributedwith regard to the delivery mode: 13 concerned a home-basedprogramme, 11 a centre-based programme, and 10 a combinedhome- and centre-based programme. Because delivery modewas pertinent to our research question, the following sectionprovides a more detailed discussion of the programmesconcerned. Most comparisons were of programmes thatincluded the coaching of parenting skills (29 out of 34). Socialor economic support was much less frequently included in thecomparisons (6 out of 34).The duration of the programmes varied greatly, viz. from 4to 96 months (average: 22 months). The intensity of theprogrammes varied from 1 to 25 hours per week (average: 8.5hours per week). Most programmes were discontinued whenstudents entered Grade 1, or earlier. Only five comparisonsconcerned programmes that were continued after kindergarten;all these were centre-based or a combination of homebasedand centre-based.

INTERNATIONAL JOURNAL OF BEHAVIORAL DEVELOPMENT, 2005, 29 (1), 35–47 41Description of programme typesAs mentioned in the Method section, we classified the earlyintervention programmes into three different programmetypes, namely home-based, centre-based, and a combinationof home- and centre-based. Each of these programme types isdiscussed below, and each programme included in the review isbriefly mentioned in order to provide a glimpse of the variety ofprogrammes.Home-based programmes. Thirteen of the comparisons concernedhome-based interventions. Of these, seven concerned aprogramme based on Hippy (Lombard, 1981). Baker, Piotrkowski,and Brooks-Gunn (1998) provided two comparisonsbased on a US Hippy programme, Kagitcibasi et al. (2001)provided three comparisons based on a Turkish Hippyadaptation, and Van Tuijl, Leseman, and Rispens (2001)provided two comparisons based on a redesign of a formerDutch Hippy adaptation. All Hippy-like programmes focusedon parents as the instructors of their children, using paraprofessionalsrecruited from the parents’ community toinstruct and support the parents, and professional coordinatorsto organise parent group-meetings. Programmes started whenchildren were between 4 and 5 years old, and lasted for 2 years(effectively 30 weeks per year). Each year, home visits weremade and group meetings were held every other week. Overthe course of the programme, parents received a series of bookswritten specifically for the Hippy programme, along withactivity packets, to which the parents were introduced duringthe home visits and group meetings. The packages focused onlanguage, problem-solving, and sensory skills, and were aimedat better preparing the children for school.The Comprehensive Child Development Program (CCDP)(Goodson et al., 2000) is a two-generation programme thatemployed case management and home visiting to providemultirisk, low-income children and their parents with a rangeof education, health, and social services. The programmeserved participating families until the child entered kindergartenor first grade. Most CCDP projects used home visits todeliver early childhood education for children between birthand the age of 3 years. The visits, which were made every 2weeks, were focused on the parents—educating them aboutchild development and teaching parenting skills—rather thanon providing services directly to children.Olds et al. (1998; Olds, Henderson, & Kitzman, 1994)evaluated the effects of a programme of prenatal and earlychildhood home visitation by nurses. The programme wasintended to avert preterm delivery and low birthweight, and—in the postpartum phase—developmental delays and behaviouralproblems. The nurses helped the women to improvetheir health-related behaviours and the quality of their infantcare-giving. Families in treatment group 3 were provided withhome visiting services during pregnancy only, while families intreatment group 4 received the same services until the child’ssecond birthday.‘‘Instapje’’ was a Dutch, parent-focused home-based programme(Riksen-Walraven, Meij, Hubbard & Zevalkink,1996) aimed at improving the quality of parental support infamilies from deprived socioeconomic backgrounds. Theprogramme was relatively short, consisting of 16 weeklyhome-visits only, starting when the child was 13 months old.Parents were supported on four behavioural dimensions:providing emotional support, respecting the child’s autonomy,structuring and limiting the child’s environment, and supportinglanguage development. The programme materials consistedof a manual for the mothers and a set of play materials tobe used with the child.The Mother Child Home Program (MCHP), implementedwith Bermudan families, was the subject of the study by Scarrand McCartney (1988). It was a widely used US earlychildhood programme that employed home visitors to demonstrateto mothers different ways of interacting with theirchildren (2- to 4-year-olds). The 2-year programme consistedof home visits made every other week. One of the key goals wasto teach mothers to be effective teachers.Wasik, Ramey, Bryant, and Sparling (1990) reported on theeffectiveness of a family education intervention programmedesigned ‘‘. . . to help the parent foster the cognitive and socialdevelopment of the child’’ (p. 1686). The programme calledfor regular home visits (weekly for the first 3 years, and thenless frequently), starting a month after the child’s birth andcontinuing throughout the preschool years. Home visitorsdiscussed ongoing concerns with parents and offered problemsolvingstrategies to cope with difficult situations.Centre-based programmes. Eleven of our comparisons concernedcentre-based interventions, each of which involved amore or less specific school curriculum. Gersten, Darch, andGleason (1988) evaluated a direct instruction curriculum,Howell et al. (1990) evaluated three preschool languagecurricula, Lee et al. (1988, 1990) evaluated generic HeadStart programmes, Slavin et al. (1990) and Madden et al.(1993) evaluated SFA, and Reynolds (1994) evaluated theCPC&EP.Most of these curricula were continued into the first threegrades, with the exception of the preschool language curriculaevaluated by Howell et al. and the Head Start programmesevaluated by Lee. The sample Lee was concerned withconsisted of children who had attended preschool in 1969/1970, which makes their evaluation valid only for Head Start asit existed about 30 years ago. Furthermore, all children in theHowell et al. study (i.e., both those in the experimental groupsand those in the control group) received Head Start, the maindifference between the groups being the supplementarylanguage curriculum they received.The other programmes in the centre-based category werebased on the idea that early intervention programmes shouldbe continued in the early grades. The direct instructionprogramme evaluated by Gersten et al.—which focused onintegrating cognitive with social development—started inkindergarten, using specific teaching materials. The authorsstressed that most of the academic content was taught throughgames and other forms of informal social interaction. However,they were less clear about the direct instruction programme inGrades 1 to 3.The SFA programme has been described in detail by Slavinet al. and Madden et al. SFA comprised half-day preschool andfull-day kindergarten programmes, with a heavy emphasis onlanguage and reading. Readiness activities included the use ofthe Peabody Language Development Kit, which the Howell etal. study also included. The reading programme in Grades 1 to3 included regrouping students into homogeneous readinggroups, increasing direct instruction time, and using readingtutors to provide one-to-one instruction. Each participatingschool favoured a family support team, providing parentingeducation and encouraging parents to support their children’s

42 BLOK ET AL. / EFFECTIVENESS OF EARLY CHILDHOOD EDUCATIONsuccess with learning. Similar to the SFA programme, theCPC&EP represented a large-scale comprehensive preschoolto Grade 3 intervention (Reynolds, 1994). This centre-basedprogramme was designed to improve children’s developmentthrough structured instructional support services, parentalinvolvement, and emphasising reading and language development.The children involved in the experimental comparisonwere in the programme for 5 years, namely from preschoolthrough Grade 3. The preschool component was a structuredhalf-day programme for 3- and 4-years-olds, and was designedto promote children’s prereading and language skills andsocioemotional development through reduced class size,parental involvement, staff training, and structured learningactivities. From kindergarten onward, the programme was afull-day programme, with similar goals and approaches.Parental involvement was realised by requiring parents toinvest at least half a day per week in the school. Parents couldchoose from a wide range of activities, such as serving asclassroom aides, tutoring children, performing clerical tasks, oraccompanying classes on field trips.Combined home- and centre-based programmes. Ten of thecomparisons concerned an intervention that combined elementsof a home- and a centre-based approach. Theseinterventions represented a wide variation of arrangements.The Houston Parent–Child Development Center (Johnson &Walker, 1987, 1991; Walker & Johnson, 1988) was designed topromote social and intellectual competence in general, and toprevent behaviour problems and school failure in particular.The programme required 550 hours of participation over a 2-year period, starting with 1-year-old children. The first year ofthe programme took place in the home and focused on themother–child interaction. Mother and child came to theproject centre during the second year to participate with otherfamilies in classes on child-rearing skills and other topicsrelated to family life.The family support intervention evaluated by Seitz et al.(1985) provided a wide range of services to parents and theirchildren. These services included social work, pediatric care,daycare, and psychological services. The programme beganduring the mother’s pregnancy and continued for 30 monthsafter birth. Daycare was provided for most of the period andwas of high quality. The staff was highly trained, and the child–caregiver ratio was three to one. Home visitors coordinated theservices provided and visited the families on average 28 timesduring the programme.The well-known Abecedarian programme was the subject ofthe evaluation reported by Ramey et al. (2000). Twocomparisons were included in our database, namely of thechildren who received the preschool programme only, and thechildren who received the preschool and the school-ageprogramme (i.e., kindergarten through Grade 2 educationalsupport). Although some of the services provided were parentdirected,the focus of the Abecedarian preschool programmewas on centre-based child education. Children participated inthe preschool programme from the age of 6 weeks until theywere 5 years old. The childcare centre was of high quality bycommon standards, and provided year-round, full-day care.Parents were provided with a programme on parenting topics,but no home visits were made. The school-age programme(from kindergarten through Grade 3) featured, in addition tothe regular school curriculum, home/school resource teacherswho tried to enhance parental involvement. Twice a week,teachers provided parents with home curriculum activitiesindividually designed for each child in order to reinforce his orher academic development.Children in the Perry Preschool Study (Schweinhart, 2000)followed a specifically designed cognitively oriented curriculumthat lasted 2 years, starting at age 3. Children participated inmorning classes, 5 days a week. The staff–child ratio was oneadult for every five or six children. Each week, the teachersmade a 90-minute home visit to the families, during which theyreviewed classroom activities and discussed similar activities inthe home.The study by Schweinhart, Weikart, and Larner (1986)resulted in three comparisons, concerning the DISTAR andthe High/Scope programme, and a traditional nursery programme.The programmes differed with respect to the degreeof initiative expected of the child and the teacher, but sharedtwo components, viz. half-day classroom sessions and educationalhome visits. A teacher visited each mother and child athome every two weeks. During these visits, the teacher tried toengage the mother in learning activities with the child,paralleling the approach used in the classroom. The programmeslasted for 2 years, starting when the children were 3years old.Project CARE was modelled on the Abecedarian project(Wasik et al., 1990). In one of the conditions in the study byWasik et al., CARE was combined with the Family Educationprogramme (which was briefly described in the section onhome-based interventions). Within CARE, children wereoffered high-quality, full-day daycare. Curriculum materialsemphasised both the cognitive and the socioemotional domain.Daycare attendance started when the children were just a fewmonths old, and continued until they entered kindergarten.The intervention programme evaluated by Whitehurst et al.(1999) was a regular Head Start programme supplementedwith an emergent literacy component. The interventionconsisted of two components, namely (1) an interactivebook-reading programme for children at home, and at schoolbased on the principles of dialogic reading, and (2) a phonemicawareness curriculum only offered at school. Both parents andteachers were taught how to read dialogically. The phonemicawareness curriculum was carried out in the second half of theschool year. The intervention encompassed the preschool year,when children were on average 4 years old. The interventiontook about 1–2 classroom hours per week, plus presumably thesame amount of time at home.Results of the meta-analysisTable 3 gives a first impression of the effect sizes at posttestingwithin the domains distinguished. Median effect sizesamounted to 0.44 for the cognitive domain and to 0.01 forthe socioemotional domain. There was one outlier, correspondingto a value of 1.88. This effect size stems from thestudy by Schweinhart et al. (1986) and concerns the differencein the cognitive domain between the DISTAR group and thecontrol group, assessed directly after the end of the treatment.Because follow-up assessments 12, 24, 36, and 60 months laterrevealed consistently large effect sizes, we rejected thepossibility of a simple error. It was decided to retain thisoutcome in the data file.Applying multilevel regression analysis, it appeared that thevariance component at the highest level (i.e., that of the study)was generally very small and was not statistically different from

INTERNATIONAL JOURNAL OF BEHAVIORAL DEVELOPMENT, 2005, 29 (1), 35–47 43Table 3Stem-and-leaf display of effect sizes at posttesting (rounded to onedecimal), including numbers and mediansStemCognitivedomainDomain/leafSocioemotionaldevelopment–0 .5–0 .001144 .00012330 .0000011111222222223333334444444444444 .001330 .55555555566666777778899 .771 .0121 .9Number 71 14Median 0.44 0.01zero in either domain. We therefore decided to remove thislevel from our models. Table 4 presents the results for the twolevelmodels without the inclusion of predictor variables. Theintegrated effect size is estimated at 0.32 (SE ¼ 0.05, p 5 .05)for the cognitive domain, which is between a small and amedium effect as defined by Cohen (1988). The integratedeffect size for the socioemotional domain is very small at 0.05(SE ¼ 0.02, p 5 .05). The variance components at both levelswere also rather small, indicating that the variance of theoutcome measures was largely a result of error variance.However, the test of homogeneity indicated for both domainsthat part of the variance was systematic.In an effort to reduce the variability of the outcomes, mostof the coded variables (except variables 19, 20, 24 and 25; seeTable 1) were introduced into the equation as predictors. Thecategorical variable ‘‘delivery mode’’ (variable 12) was recodedinto dummy variables. Additionally, an extra predictor variablewas composed by multiplying the length of the programme(variable 13) by the intensity of the programme (variable 14).This new variable—‘‘Dose’’—represents more or less the totalintervention effort. Characteristics of the outcome measures,experimental comparisons, and studies were progressivelyTable 4Parameter estimates for the start model without predictors in twodomainsCognitivedomain(n ¼ 71)Socioemotionaldevelopment(n ¼ 14)Parameters Coeff. SE Coeff. SEFixed effectsIntegrated effect size 0.32* 0.05 0.05* 0.02Random effectsVariance betweenexperimentalcomparisonsVariance betweentimes ofmeasurement0.06*0.03*0.020.010.000.000.000.00Test of homogeneity Q ¼ 599.45*, df ¼ 70 Q ¼ 80.87*, df ¼ 13* Effects statistically different from zero (p 5 .05).entered as predictors, starting with the characteristic thatshowed the strongest association, and proceeding with the nextbest predictor. The addition of characteristics was halted whenno predictor could be found that significantly decreased theheterogeneity of the effect sizes. This search for predictors wasperformed separately for both domains. The resulting modelswere considered to be the final ones (Table 5). Both modelsappeared to be stable, as a back-tracking procedure (startingwith all possible predictors and progressively deleting theweakest predictor) led to the same results.The final models for the cognitive and the socioemotionaldomain both contained some unexplained variance, asindicated by the test of homogeneity. However, none of thevariance components was statistically different from zero, asthey were smaller than twice their standard errors.The interpretation of the regression coefficients is relativelystraightforward, because the coefficients were not standardisedand dichotomous variables were coded as either 0 (characteristicnot present) or 1 (characteristic present). In the cognitivedomain, the regression weights for the dummy variables for thecentre-based and the combined home- and centre-baseddelivery indicated an advantage of about 0.4 to 0.5 SD overhome-based programmes. In the socioemotional domain, onlya small negative effect could be demonstrated for home-basedprogrammes. However, this effect of 0.05 SD is not significantlydifferent from zero. One other single programmecharacteristic turned up as a significant predictor: programmesthat included the coaching of parenting skills had a positiveeffect on outcomes in the cognitive domain (of about 0.7 SD),but not in the socioemotional domain.Three other significant predictors in the cognitive domainrepresented characteristics of the study design. Using a controlgroup following no programme at all (or following an unknownprogramme) increased the results by about 0.25 SD. Usinggain scores or a design with covariates decreased the results by,again, 0.25 SD. Positive effect sizes at pretesting wereassociated with higher effect sizes at posttesting.Finally, the time of measurement exerted a small, butsignificant, negative effect of –0.03 (SE ¼ 0.01) on outcomesin the cognitive domain, indicating that, on average, effect sizesdiminished by 0.03 SD for each consecutive year. This effectmight be interpreted as a representation of the fading ofoutcomes over time.DiscussionEarly intervention programmes generally tend to be moderatelyeffective in the cognitive domain, but not in thesocioemotional domain. The raw overall effect size was equalto 0.3 SD in the cognitive domain and to nearly zero in thesocioemotional domain. Two programme characteristics werefound to be related to outcome measures, but only in thecognitive domain: the delivery mode and the inclusion of thecoaching of parenting skills. Home-based programmes wereabout 0.5 SD less effective than both centre-based programmesand combined home- and centre-based programmes. Theinclusion of parenting skills support had a particularly strongeffect on outcomes (0.7 SD). Several other programmecharacteristics—including programme recency, programmelength, programme intensity, total programme dose, children’sage at programme onset, continuation of programme after

44 BLOK ET AL. / EFFECTIVENESS OF EARLY CHILDHOOD EDUCATIONTable 5Parameter estimates for the final model in two domainsCognitivedomain(n ¼ 71)Socioemotionaldevelopment(n ¼ 14)Parameters Coeff. SE Coeff. SEFixed effectsIntegrated effect sizeIntervention in control group (Var. 3)Dummy centre-based (Var. 12) aDummy combined home-/centre-based (Var. 12) aDummy home-based (Var. 12) aInclusion of coaching of parenting skills (Var. 17)Effect size at pretest (Var. 18)Time of measurement (Var. 21)Type of posttest score (Var. 22)Random effectsVariance between experimental comparisonsVariance between times of measurement–1.02*0.24*0.48*0.42*—0.69*0.63*–0.03*-0.22*0.220.070.090.08—0.110.190.010.070.08*———–0.05————0.03———0.04————0.010.010.010.010.000.000.000.00Test of homogeneity Q ¼ 166.80*, df ¼ 63 Q ¼ 76.64*, df ¼ 12— indicates parameter not specified. See Table 1 for the interpretation of the variables.a The variable delivery mode (Var. 12) was replaced by dummy variables.* Effects statistically different from zero (p 5 .05).kindergarten, and provision of social or economic support toparents—showed no relationship with outcome measures.Further, the longitudinal nature of the available outcomemeasures allowed us to estimate the fading of outcomes afterending of interventions. This effect amounted to 0.03 SD peryear. Finally, effect sizes were also moderated by three studydesign characteristics, namely whether or not the control grouphad followed a standard programme, the difference betweenthe experimental and the control group at pretesting, and theuse of gain scores rather than observed scores.The results of our meta-analysis confirm quantitatively theconclusions reached in narrative syntheses regarding theconsiderably stronger efficacy of centre-based programmes orcombined centre- and home-based programmes in thecognitive domain (Barnett, 1995; Bowerman et al., 2001;Farran, 2000; McGuire & Earls, 1991; Ramey & Ramey,1998). The results show that the outcomes of these programmesare about 0.5 SD larger than those of home-basedprogrammes. The overall effectiveness of early interventionprogrammes with an educational orientation appeared to benear zero in the socioemotional domain. The results of thisstudy do not confirm the particular importance of a combinedintervention for obtaining effects in this domain as well(Yoshikawa, 1994).Our analyses revealed no evidence of a unique contributionto programme outcomes of age of onset, duration, intensityand dose of the programme, or forms of parental and familysupport, with the exception of the provision of parenting skills.This seems to contradict conclusions resulting from previousnarrative syntheses (Barnett, 1995; Bryant & Maxwell, 1997;McGuire & Earls, 1991), and those presented in quantitativereviews (Leseman, Otter, Blok, & Deckers, 1998; Royce,Darlington, & Murray, 1983) and as theoretical considerations(Rutter, 2000). A possible explanation for this is that in theseother studies, which focused mostly on bivariate relationships,there may have been confounding between these programmecharacteristics and the delivery format. Recency of theprogramme, onset age, and programme duration appearednot to be significantly related to the delivery mode. However,centre-based and combined home- and centre-based programmeswere on average much more intensive, and thereforeprovided a clearly higher dose of intervention than home-basedprogrammes did. Correlations of a dummy variable denotingcentre-based and combined home- and centre-based programmesversus home-based programmes with intensityamounted to .76 (p 5 .001) and with dose to .47 (p 5.01). Therefore, the importance of programme intensity andprogramme dose may be masked, at least partly, by deliverymode.No effect of the continuation of the preschool interventioninto elementary school was found in addition to the effect ofbasic delivery strategy, which seems to contradict in particularthe rather robust findings of three major studies included in thepresent analysis, namely those concerning the CPC&EP, thepreschool plus K2 version of the Abecedarian project, and theextensions of the SFA programme into the lower grades. Froma theoretical perspective, enhancing continuity upon transitionsbetween the most important social contexts of the youngchild (i.e., home, preschool, and elementary school) seems veryimportant to optimise developmental and learning gains(Rimm-Kaufman & Pianta, 2000). Again, confounding withdelivery strategy may be a possible explanation for the lack ofsuch effect in the present meta-analysis. No home-basedprogramme in the present selection was continued afterkindergarten or transferred into the first grade of elementaryschool. This notwithstanding, however, it seems a distinctpossibility that the previously reported significance of continuingpreschool interventions into elementary school holds onlyfor the particular programmes for which this effect has beenfound.

INTERNATIONAL JOURNAL OF BEHAVIORAL DEVELOPMENT, 2005, 29 (1), 35–47 45In summary, centre-based and combined centre- and homebasedprogrammes were on average characterised by a higherintensity and thus a higher dose of the intervention than werehome-based programmes, and they also appeared to be moreoften continued into elementary school. These three featureswere related to programme efficacy in previous narrativereviews. As we could estimate models in which all predictorswere included, we found delivery mode to be the betterpredictor, leaving no room for unique contributions from otherprogramme characteristics, except the inclusion of parentingcoaching. Particularly important in the present results was theadditional strong effect of including the coaching of parentingand parenting skills, which was found to increase the effect sizein the cognitive domain by 0.7 SD.The studies reviewed did not provide detailed informationon how parenting coaching and parenting skill training affectedprogramme outcomes. Therefore some possible mechanismswill be briefly discussed here. Several studies have pointed tothe importance of an emotionally supportive home environmentfor cognitive gains from education in preschool andkindergarten (Pianta, Nimetz, & Bennett, 1997; van IJzendoorn,Sagi & Lambermon, 1992). What seems to be crucial isthe child’s trust in social relationships, which transfers from thehome to the centre or school. Parenting coaching in theincluded programmes may have improved emotional supportin the family and attachment to others (Van Tuijl & Leseman,2004). A different explanation is that programmes withparenting coaching have effectively counteracted the frequentlyreported problems with programme implementation in highriskgroups, varying from irregular attendance to the reluctanceof parents to participate in parental activities or to work withthe child at home (Farran, 2000). This may explain why thecoaching of parents to provide the support needed (e.g.,bringing children to the centre on time, well-rested, and wellnurtured;attending parent–teacher conferences) is associatedwith positive child outcomes.In contrast to the effect of parenting skills training, no sucheffect was found for the inclusion of a social, health, oreconomic family support component. Note, however, that thistype of parent and family support may yield important effectsin other outcome measures, such as the long-term preventionof child abuse and neglect (MacLeod & Nelson, 2000), and theprevention of health problems, emotional problems, andconduct disorders in adolescence (Olds et al., 1998; Olds &Kitzman, 1993). Although these outcomes may not be directlyrelevant to short-term cognitive or socioemotional goals, theymay modulate in particular the preservation of early effects upinto adulthood and their transformation into life-phaserelevantoutcomes, such as social adjustment, economicindependence, and positive health behaviour (Yoshikawa,1994).Programme effects do fade over time. Our results confirmprevious observations of this phenomenon and have resulted ina robust quantitative estimate. The mean linear decrease of theeffect size based on the nine studies that reported mediumlong-term and long-term follow-up results, covering all types ofprogrammes, was estimated at 0.03 SD per year, which is lessthan previously reported (Blok & Leseman, 1996; McKey etal., 1985). Based on this, it would take 10 years for animmediate programme effect of d ¼ 0.3 (the average effectfound in this study) to completely disappear. According toMcKey et al., who based their conclusions on Head Startevaluation studies conducted before 1982, this would be about2 years. Our selection included more studies with long-termfollow-up measurements than previous reviews did, even up to15 years after withdrawing the intervention (Olds et al., 1998).An important consideration is that the decrease in effect sizemay be nonlinear, with a stronger decrease in the first few yearsafter the intervention, but a less strong decrease in subsequentyears, as hypothesised by Ramey et al. (2000). Many morelong-term outcomes will be needed to test this hypothesis.Few studies in the present meta-analysis—focusing onprogrammes with an educational orientation—reported outcomesin the socio-emotional domain. This finding, which maybe related with our search and selection strategy, seems toreflect the predominant cognitive orientation of early childhoodintervention programmes, despite the growing recognitionof the strong interrelatedness of motivation, emotionallybased self-regulation, and cognitive learning in educationprogrammes (Barnett, Young, & Schweinhart, 1998; Boekaerts,1999). The selected studies that did include socioemotionaloutcome measures revealed a much smaller overalleffect size than was found for cognitive outcomes. However, nostrong negative effects were reported in the studies weinvestigated, in contradiction to the results of Haskins (1985)on early centre-based education programmes with a strongcognitive emphasis, and to the recent findings of the EarlyChildcare Network of the National Institute of Child Healthand Human Development (NICHD) regarding intensive,early-onset centre-based care (NICHD, 2002). Nonetheless,the observation that early intervention programmes with aneducational orientation do not seem to have an impact on thesocioemotional development is worrying, given the interrelatednessof motivational, emotional, and cognitive processes inpost-intervention school learning. The competition betweensocioemotional and cognitive-academic goals is also at theheart of the debate on developmentally appropriate versusdidactic practices in early childhood education (Marcon, 1999;Schweinhart & Weikart, 1997; Stipek, Feiler, Daniels, &Milburn, 1995).Our study does not indicate programme design characteristicsthat are related to socioemotional outcomes for earlyintervention programmes with an educational orientation. Thisleaves us with the question how future programmes of this typeshould be designed to achieve positive effects in the socioemotionaldomain. An interesting programme characteristic inthis respect may be the programmes’ pedagogical processes(e.g., child-centred versus teacher-directed, developmentalversus didactic curriculum). As noted earlier, the programmedesign characteristics explored here do not fully explain thevariation in effect sizes. The process characteristics alluded tohere are obvious candidates to explain the still unexplainedvariation in outcomes. Unfortunately, few studies providesufficient details about the daily processes and teacher–childinteractions to determine the impact of different pedagogicalmodels on cognitive and socioemotional outcomes.Finally, our results have two more or less clear implicationsregarding the format or delivery of future programmes. Thefindings provide a strong argument for the delivery ofprogrammes in a centre or a combined centre- and homebasedformat. Furthermore, the findings suggest to include aparenting skills component, although this probably will onlyaffect the cognitive development of children, but not theirsocioemotional abilities. It is difficult to formulate furtherimplications with regard to programme intensity and length,continuation after kindergarten, and the target age of children,

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