We present results from a meta-analysis of 37 experimental and quasi-experimental studies of summer programs in mathematics for children in grades pre-K-12, examining what resources and characteristics relate to stronger student achievement, attainment, and social-emotional and behavioral outcomes. Compared to control group children, children who participated in summer programs that included mathematics lessons and activities enjoyed significant improvements in mathematics learning as well as social-behavioral outcomes. We find an average weighted impact estimate of +0.09 standard deviations on mathematics achievement outcomes. In a parallel meta-analysis, we found similar positive impacts of summer programs on socialemotional and behavioral outcomes, Programs conducted in both high- and lower-poverty settings saw similar positive impacts. The results highlight the potential for summer programs to strengthen children’s mathematical ability and improve learning outcomes in both mixed-poverty and high-poverty settings. (author abstract)