There is an increasing prevalence of overweight in preadolescents that predicts physical problems over the lifespan. Physical inactivity has been implicated as an associated factor, with African American youth being at an increased risk. Based on social cognitive theory, and proposed correlates of physical activity in youth, changes over 12 weeks in measures of self-appraisal (general self, physical appearance, physical self-concept, exercise barriers self-efficacy) and mood (tension, vigor), and their relations with voluntary physical activity changes, were assessed within an after-school care physical activity intervention. Participants were volunteers recruited from children already registered for a 12-week segment of YMCA after-school care. The treatment group consisted of 146 African American preadolescents with the control group comprised of 123 African American preadolescents who were scheduled to receive the program during the next sequence that it was offered. Results indicated the intervention group reported significantly more positive self-appraisals, reduced tension, and enhanced vigor. Bivariate and multiple regression analyses indicated that when each of the 4 self-appraisal and 2 mood factors were simultaneously entered into a regression equation, 36% of the variance in voluntary physical activity was explained. Findings support the treatment's association with theoretically based correlates of physical activity in the present sample, and suggest directions for physical activity interventions for youth. ©Journal of Sports Science and Medicine.