Most children and adolescents do not meet the recommended 60 minutes or more of moderate to vigorous physical activity per day. One attractive approach to increasing physical activity in young people is providing activity through structured after-school programs. This paper provides a review of the scientific literature on the effects of after-school programs on physical activity in children and adolescents. After-school physical activity interventions provided mixed results; some increased children’s physical activity, others did not. Although after-school programs have the potential to help children and adolescents engage in regular, enjoyable physical activity, the research on these programs is limited and, in some cases, methodologically weak. Additional, well-controlled studies are needed to identify the components of after-school programs that promote physical activity and to determine the level of activity that can be attained when children and adolescents participate in these programs.