Background: Most youth in the United States do not meet the recommended 60 minutes of daily physical activity (PA). The school environment offers an opportunity to engage students in PA. The purpose of this study was to evaluate the impact of a comprehensive school-based physical activity program on student PA across student-level and school-level characteristics. Methods: PA levels from 3294 fourth grade students in 24 intervention schools and 7 control schools in metropolitan Atlanta, Georgia were measured during the 2015-2016 academic year. PA measures included daily steps in school, steps taken in physical education class (PE), and percent of PE class time spent in moderate-to-vigorous physical activity (MVPA). Intervention effectiveness was assessed using generalized estimating equations adjusting for sex and school-level socioeconomic status (SES). Results: After adjusting for sex and school-level SES, intervention students had significantly higher increases in average daily steps (p [less than]0.05), steps taken in PE (p [less than] 0.01), and percent of PE class spent in MVPA (p [less than] 0.01) than control students. Conclusion: Our findings demonstrate the effectiveness of CSPAPs in increasing PA. Further research using randomized controlled trials of large-scale implementations, longer follow-up periods, and more diverse student sample is warranted.