How should we measure the effect of ability grouping on student performance?

In this volume, Betts and Shkolnik [Betts, J. R., & Shkolnik, J. L. (1999) The effects of ability grouping on student math achievement and resource allocation in secondary schools. Economics of Education Review, 19, 1-15] argue that studies that compare students in tracked versus untracked classes overestimate the impact of tracking on student achievement by not adequately controlling for student ability and motivation. In this paper we discuss the shortcomings of their analysis and reinterpret their results. The data used by Betts and Shkolnik do not allow one to accurately classify tracked and untracked classroom, since identification of heterogeneous classes is impossible. They compare ability-grouped students in schools that report formally engaging in tracking to ability-grouped students in schools that track only informally. Our interpretation of their results suggests that there is little difference in student performance and resource allocation between schools that formally and informally group students by ability.[JEL I20].