Background: Two Healthy People 2020 goals are to increase physical activity (PA) and to reduce disparities in PA. We explored whether PA at the school level changed over time in Minnesota schools and whether differences existed by demographic and socioeconomic factors. Methods: We examine self-reported PA (n = 276,089 students; N = 276 schools) for 2001–2010 from the Minnesota Student Survey linked to school demographic data from the National Center for Education Statistics and the Rural–Urban Commuting Area Codes. We conducted analyses at the school level using multivariable linear regression with cluster-robust recommendation errors. Results: Overall, students who met PA recommendations increased from 59.8% in 2001 to 66.3% in 2010 (P < .001). Large gains in PA occurred at schools with fewer racial/ethnic minority students (0%–60.1% in 2001 to 67.5% in 2010, P < .001), whereas gains in PA were comparatively small at schools with a high proportion of racial/ethnic minority students in 2001 (30%–59.2% in 2001 to 62.7% in 2010). Conclusions: We found increasing inequalities in school-level PA by racial/ethnic characteristics of their schools and communities among secondary school students. Future research should monitor patterns of PA over time and explore mechanisms for patterns of inequality.