Supporters of single‐sex schooling believe that separating boys and girls, by classrooms or schools, increases students' academic achievement. Critics of single‐sex schooling believe that gender segregation increases students' gender stereotypes and has no effect on students' achievement. In this article, we present these rationales, focusing on developmental issues that may affect the effectiveness of single‐sex schooling. We then review the research on the effectiveness of single‐sex schooling. Overall, findings suggest that single‐sex schooling is not more effective than coeducational schooling at improving students' academic achievement or attitudes. More work is needed to explore a broader range of outcomes, examine developmental factors that may influence the effectiveness of various types of schooling, and communicate results to parents, educators, and policymakers.