This policy brief reviews research on the effectiveness of summer-school programs. It begins with a short history of the current school calendar, including how 19th century agrarian life required children to stay home during the summer to attend to crops or livestock. Next, a meta-analysis of 13 studies brings to light the effects long summer breaks have on students, such as the loss of 1 month on achievement test scores, and the significant loss of math and spelling skills. A history of summer school and summer-school goals follows. Goals include preventing delinquent behavior, remediating or preventing learning deficits, helping to meet minimum competency requirements, breaking the poverty cycle, and accelerating progress for gifted students. A review of research on summer school's effectiveness follows, which demonstrates a dominantly positive effect on students. The brief concludes with recommendations that policymakers should continue to fund summer-school programs, require that funds for summer school be spent on mathematics and reading instruction, and set aside funds for the purpose of fostering participation in summer programs, especially by disadvantaged students. Practitioners should plan early, provide program and staffing continuity from year to year, and integrate summer teaching with staff development. (Contains 18 references.) (RT)