This policy brief draws on research and evaluations of efforts in Tennessee, California, and Wisconsin to describe different approaches to reducing class size in kindergarten through third grade. Tennessee implemented a randomized experiment to investigate the effectiveness of smaller classes; California used a statewide approach; and Wisconsin targeted class-size reduction as part of an effort to increase achievement in high-poverty schools. Tennessee's STAR program provides the strongest evidence that smaller class sizes improve student performance. California's experiment showed much smaller improvements in student achievement compared with Tennessee's. Wisconsin's SAGE program produced larger increases in achievement in mathematics and language arts than California obtained, but less than were found in Tennessee. Evidence from these states provides guidance for policymakers about whether and how to implement a class-size-reduction program. The brief considers questions such as: What makes small classes more effective? How small is small and for how long? and How much does it cost to reduce class size? Other topics include key cost considerations, funding and fiscal equity, long-term costs, finding teachers for additional classrooms, finding additional classroom space, and crafting class size to meet education needs. The brief concludes with a list of nine resources. (RT)