Formative assessment is a process that engages teachers and students in gathering, interpreting, and using evidence about what and how students are learning. This review identifies rigorous studies of the effectiveness of formative assessment on elementary school student achievement. Results of the review indicate that overall, formative assessment had a positive effect on student academic achievement. On average across the studies, students who participated in formative assessment performed better on measures of academic achievement than those who did not. Formative assessment used during math instruction had larger effects, on average, than did formative assessment used during reading and writing instruction. For math, both student-directed formative assessment and formative assessment directed by other agents, such as an educator or a computer program, were effective. For reading, other-directed formative assessment was more effective than student-directed formative assessment.