Research Commentary: The Effects of Spacing and Mixing Practice Problems

Sets of mathematics problems are generally arranged in 1 of 2 ways. With blocked practice , all problems are drawn from the preceding lesson. With mixed review , students encounter a mixture of problems drawn from different lessons. Mixed review has 2 features that distinguish it from blocked practice: Practice problems on the same topic are distributed, or spaced, across many practice sets; and problems on different topics are intermixed within each practice set. A review of the relevant experimental data finds that each feature typically boosts subsequent performance, often by large amounts, although for different reasons. Spacing provides review that improves longterm retention, and mixing improves students' ability to pair a problem with the appropriate concept or procedure. Hence, although mixed review is more demanding than blocked practice, because students cannot assume that every problem is based on the immediately preceding lesson, the apparent benefits of mixed review suggest that this easily adopted strategy is underused.