LAUSR

Abstract Over the past two decades educational research has become increasingly interested in the development of children's adaptive expertise in arithmetic. Even though there are several studies investigating the impact of different teaching approaches, knowledge concerning effects of learning resources is relatively low. Using data of a three-year longitudinal study with 1404 students from 82 classes, we examined learning opportunities presented by textbooks regarding adaptive expertise in multi-digit addition and subtraction, and in a subsequent multilevel analysis, the effect of the resulting textbook quality on third-graders' adaptive expertise. The results show discrepancies in the textbooks' quality concerning learning opportunities for adaptive expertise and a substantial effect of textbook quality on students' adaptive expertise after three years of schooling. An additional cross-level interaction suggests that the effect of textbook quality increases with children's prior arithmetic knowledge.