Purpose: Although a physically active lifestyle plays an important role in maintaining and maximizing physical and mental health, most school students are not physically active on a regular basis (USDHHS, 2000). The youth physical activity promotion (YPAP) model outlines a social ecological approach whereby personal, social environmental, and physical environmental factors may respectively predispose, reinforce, or enable youth to be physically active (Welk, 1999). Although the YPAP model provides an innovative theoretical framework with regard to important correlates of physical activity (PA) behavior change, limited data-based evidence exists to support this model. The purpose of this study was to investigate the predictive strength of the predisposing personal factors (self-efficacy in PA, enjoyment of PA), reinforcing social environmental factors (parents' support and friends' support), and enabling physical environmental factors (equipment accessibility and neighborhood safety) on leisure-time PA and team sport participation. Methods: Participants were 286 middle school students (143 boys; 143 girls; M age = 13.36). Previously validated questionnaires were used to assess participants' perceptions of self-efficacy, enjoyment, social support from parents and friends, equipment accessibility, neighborhood safety, leisure-time PA, and team sport participation. Pearson correlations were used to examine the relationships among the variables. Two hierarchical regression analyses were conducted to determine the predictive strength of the personal factors (block 1), social environmental factors (block 2), and physical environmental factors (block 3) on leisure-time PA and team sport participation, respectively. Analysis/Results: Correlation analyses revealed there were positive relationships among all the variables. The first hierarchical regression analysis revealed self-efficacy (β = .23, p< .01) and parents' support (β = .15, p< .05) were important predictors of leisure-time PA (η2 = 15.8 %). The second regression analysis indicated parents' support (β = .26, p< .01), friends' support (β = .17, p< .05), and neighborhood safety (β = .15, p< .05) significantly predicted team sport participation (η2 = 14.7%). Conclusions: Based on the study findings, health promoters can develop leisure-time PA motivational programs for school students based on personal and social environmental factors. Additionally, they can develop motivational programs targeting team sport participation based on social and physical environmental factors. The findings support the assertion that the YPAP model is a useful framework for investigating PA behaviors among school students. Additional investigation is needed to determine how, based on this model, interventions can be designed to structure the social and physical environments in schools to promote leisure-time PA behaviors.