Reducing class size is a popular education policy measure with parents, teachers, and policymakers. However, research shows that reducing class size leads to, in most cases, only modest improvements in student achievement. Also, students in early grades appear to gain more from smaller classes than older students. Despite extensive research on class size, much about this relationship is still unknown. Policymakers should be aware that reducing class sizes can be costly, is no guarantee of improved achievement, and is only one of many possible reforms.