Limited intervention success in increasing and sustaining girls' moderate-to-vigorous physical activity (MVPA) underscores a need for continued research. The aim of this study was to evaluate the effect of a 17-week Girls on the Move (GOTM) intervention on increasing MVPA among fifth- to eighth-grade girls. This study is a group (cluster) randomized trial, including 24 schools, pair matched and assigned to intervention (n = 12) or control (n = 12) conditions. Participants included 1,519 girls in racially diverse public schools in urban, underserved areas of the Midwestern USA. The intervention included three components: (i) 90-min after-school physical activity (PA) club offered 3 days/week; (ii) two motivational, individually tailored counseling sessions; and (iii) an interactive Internet-based session at the midpoint of the intervention. Main outcome measures were weighted mean minutes of MVPA per week post-intervention and at 9-month follow-up measured via accelerometer. No between-group differences occurred for weighted mean minutes of MVPA per week at post-intervention (B = -0.08, p = .207) or 9-month follow-up (B = -0.09, p = .118) while controlling for baseline MVPA. Research is needed to identify interventions that assist girls in attaining and maintaining adequate PA. NCT01503333.