Abstracts - Earli

preferential strategy on each item, and two no-choice conditions, wherein they had to solve allitems with either direct subtraction or indirect addition strategies. Results indicate that adults applyboth direct subtraction and indirect addition strategies on three-digit subtractions, and fit theirstrategy choices flexibly to both item and strategy performance characteristics. These resultsprovide empirical evidence for the validity of the multiple-procedures view, and of recenttheoretical models on adaptive strategy choices, in the domain of multi-digit arithmetic. Moreover,indirect addition strategies were most efficient on multi-digit subtractions. This result sheds newlight on current instructional practices, focusing on the mastery of direct subtraction strategies onmulti-digit subtractions.Mistake-handling activities in the mathematics classroom: Effects of an in-service teacher trainingon students’ performance in geometryAiso Heinze, University of Munich, GermanyKristina Reiss, University of Munich, GermanyFor many students’ and teachers’ mistakes are associated with negative feelings. Despite the factthat „mistakes are the best teachers", according to a well-known everyday proverb, teachers andstudent hardly take advantage of mistakes in the learning processes (Heinze, 2005). Thus weinvestigated the effects of teacher training on the role of mistakes in the learning of mathematics.We used a quasi-experimental design with 619 students from 29 classrooms in grades 7/8.Teachers of an experimental group received a combined training to learn from mistakes and toteach reasoning and proof, whereas the teachers of the control group only had training in reasoningand proof. Their students took part in a pre-test with reasoning and proof tasks, and in acorresponding post-test that was conducted two months after teacher training. Moreover, thestudents were asked to evaluate how the teachers handled their mistakes. Our findings show thatthe teacher training was successful under two aspects: On the one hand, the teacher of theexperimental group changed their behavior as far as the handling of mistakes was concerned. Thiswas done in a manner that was recognized by their students. The difference between experimentaland control group indicated moderate effects. On the other hand, compared to the students in thecontrol group the students in the experimental group performed significantly better in geometrypost-test. In particular, their improvement was based on a better performance on proof itemsasking for high competency.The role played by the classroom in determining curriculum enactmentTammy Eisenmann, weizmann Institute of Science, IsraelRuhama Even, weizmann Institute of Science, IsraelThe aim of this study is to investigate the role played by the classroom in determining curriculumenactment. The study addresses this issue by comparing and contrasting the types of algebraicactivities (Kieran, 2004) enacted in two classes taught by the same teacher. The researchcomprises two case studies. Each case includes one teacher who teaches two 7th grade classes;each from a school with a different socio-cultural background. The same textbook is used in allfour classes. Holding constant both the textbook and the teacher aim to provide information on therole played by the classroom in determining the enacted curriculum. Data sources includeobservations of the same learning unit in each class and interviews with the teachers and thestudents. Data are analyzed both quantitatively and qualitatively. Using Chi-square test, wecompared the distributions of algebraic activity types in the textbook and in each enactedcurriculum. Common methods of qualitative research were used to suggest explanations for thedifferences found. The findings of this study show that in both cases there was more emphasis on– 735 –