This report is the first of several to come from CASEL's major meta-analysis project. The report describes the strong positive effects after-school programs can have, and the conditions needed to realize these benefits. A meta-analysis to evaluate the magnitude of effects obtained from 73 programs was conducted. Outcomes were examined in three general areas: feelings and attitudes, indicators of behavioral adjustment, and school performance. Highlighted findings include: (1) Youth who participate in after-school programs that promote personal and social skills benefit across all three outcomes; and (2) It was possible to identify effective programs. Three appendixes are included: (1) Bibliography of Reviewed Reports; (2) Program Notes; and (3) Tables Showing Effect Size by Outcome Category. (Contains 7 footnotes and 10 tables.)