This research brief draws on seminal research and evaluation studies to address two primary questions: (a) Does participation in after school programs make a difference, and, if so (b) what conditions appear to be necessary to achieve positive results? The brief concludes with a set of questions to spur conversation about the evolving role of after school in efforts to expand time and opportunities for children and youth in the 21st century. (Contains 60 notes.) [Additional funding for this brief was provided by The Wallace Foundation.]