OBJECTIVES: To assess the accessibility and suitability of schools as recreational sites and to determine whether they are associated with young adolescent girls' weekend metabolic equivalent-weighted moderate-to-vigorous physical activity and body mass index (BMI). METHODS: The authors drew a half-mile (0.805 km) radius around the residences of participants in the Trial of Activity for Adolescent Girls (n = 1556) in Maryland, South Carolina, Minnesota, Louisiana, California, and Arizona. The authors visited all schools and parks within the defined distance and documented their amenities and accessibility on Saturdays in Spring 2003. Staff gathered data on each girls' height and weight and used accelerometers to record weekend metabolic equivalent-weighted moderate-to-vigorous physical activity. RESULTS: Schools represented 44% of potential neighborhood sites for physical activity. However, a third of schools were inaccessible on the Saturday the authors visited. Neighborhoods with locked schools were primarily non-white, older, more densely populated, and of lower socioeconomic status. Though there was no relationship between school accessibility on Saturdays and weekend metabolic equivalent-weighted moderate-to-vigorous physical activity, the number of locked schools was associated with significantly higher body mass index. CONCLUSIONS: The lack of relationship between metabolic equivalent-weighted moderate-to-vigorous physical activity and school accessibility may imply that young adolescent girls do not identify schools as recreational resources. However, due to the association between body mass index and locked schools, efforts to stem the obesity epidemic should include making schools more accessible.