Research evidence suggests that summer breaks contribute to income-based achievement and opportunity gaps for children and youth. However, summertime can also be used to provide programs that support an array of goals for children and youth, including improved academic achievement, physical health, mental health, social and emotional well-being, the acquisition of skills, and the development of interests. This report is intended to provide practitioners, policymakers, and funders current information about the effectiveness of summer programs designed for children and youth entering grades K-12. Policymakers increasingly expect that the creation of and investment in summer programs will be based on research evidence. Notably, the 2015 Every Student Succeeds Act (ESSA) directs schools and districts to adopt programs that are supported by research evidence if those programs are funded by specific federal streams. Although summer programs can benefit children and youth who attend, not all programs result in improved outcomes. RAND researchers identified 43 summer programs with positive outcomes that met the top three tiers of ESSA's evidence standards. These programs were identified through an initial literature search of 3,671 citations and a full-text review of 1,360 documents and address academic learning, learning at home, social and emotional well-being, and employment and career outcomes. The authors summarize the evidence and provide detailed information on each of the 43 programs, focusing on the evidence linking summer programs with outcomes and classifying the programs according to the top three evidence tiers (strong, moderate, or promising evidence) consistent with ESSA and subsequent federal regulatory guidance.