Organization, Instruction, and the Effects of Ability Grouping: Comment on Slavin’s “Best-Evidence Synthesis”

Slavin’s best-evidence synthesis of ability grouping research is a competent and useful summarization of existing research. But the synthesis is limited by the conceptual inadequacy of the studies it reviews. This comment argues that ability-grouping researchers must distinguish between school and classroom organization, on the one hand, and classroom instruction on the other. Instruction may serve as a key mechanism through which ability grouping has its effects. Other mediating conditions also need to be considered. Knowledge of intervening circumstances is essential in order to measure and understand the effects of ability grouping.