Bell Curve

406 Living to get he^IQ gains attributable to the Consortium preschool projectsMedian gain in IQ points8 -1 -O Exit test 1 year 2 years 3 yearsPeriod After the End of the ProgramSource: Lazar and Darlington 1982, Table 15.children who are considered to be at high risk of mental retardation,based on their mothers' low IQs and socioeconomic deprivation.A case can be made for expecting interventions to be especially effectivefor these children, since their environments are so poor that theyare unlikely to have had any of the benefits that a good program wouldprovide. Moreover, if the studies have control groups and are reasonablywell documented, there is at least a hope of deciding whether theprograms succeeded in forestalling the emergence of retardation. Wewill briefly characterize the two studies approximating these conditionsthat have received the most scientific and media attention.THE ABECEDARIAN PROJECT. The Carolina Abecedarian Project startedin the early 1970s, under the guidance of Craig Ramey and his associates,then at the University of North Car~lina.~ Through various socialagencies, they located pregnant women whose children would be athigh risk for retardation. As the babies were born, the ones with obviousneurologic disorders were excluded from the study, but the remainderwere assigned to two groups, presumably randomly. In all, there werefour cohorts of experimental and control children. Both groups of babiesand their families received a variety of medical and social work services,but one group of babies (the"experimentals") went into a day careRaising Cognitive Ability 407program. The program started when the babies were just over a monthold, and it provided care for six to eight hours a day, five days a week,fifty weeks a year, emphasizing cognitive enrichment activities withteacher-to-child ratios of one to three for infants and one to four to oneto six in later years, until the children reached the age of 5. It also includedenriched nutrition and medical attention until the infants were18 months old.69 he Abecedarian Project is the apotheosis of the daycare approach. This is extremely useful from a methodological perspective:Even if the nation cannot afford to supply the same services to theentire national population of children who qualified for the AbecedarianProject, it serves as a way of defining the outer limit of what day carecan accomplish given the current state of the art.At the end of the fifth year, the children receiving the day careoutscored those who did not by half a standard deviation on an intelligencetest. At last report, the children were 12 years old and were stilldoing better intellectually than the controls. Combining all the cohorts,only 28 percent of the experimental children had repeated a grade, comparedto 55 percent of the control children. Only 13 percent of the experimentalchildren had IQs of less than 85, compared to 44 percent ofthe control ~hildren.~'This would be unequivocal good news, except for charges that thetwo groups were not comparable in their intellectual prospects at birth.Ignoring the more technical issues, the major stumbling block to decidingwhat the Abecedarian Project has accomplished is that the experimentalchildren had already outscored the controls on cognitiveperformance tests by at least as large a margin (in standard score units)by the age of 1 or 2 years, and perhaps even by 6 months, as they hadafter nearly five years of intensive day care.17" There are two main explanationsfor this anomaly. Perhaps the intervention had achieved allits effects in the first months or the first year of the project (which, iftrue, would have important policy implications). Or perhaps the ex-~erimental and control groups were different to begin with (the samplesizes for any of the experimental or control groups was no larger thanfifteen and as small as nine, so random selection with such small numbersgives no guarantee that the experimental and control groups willbe equivalent). To make things still more uncertain, test scores for childrenyounger than 3 years are poor predictors of later intelligence testscores, and test results for infants at the age of 3 or 6 months are ex-