Minimal effects found across youth physical activity (PA) interventions, and increased attention to circumstances that impede adequate delivery of program components, has highlighted the importance of learning from staff what is needed to foster staff comprehension and engagement for developing, adopting, and successfully implementing PA-based youth interventions. The purpose of this study is to address this knowledge gap by conducting a qualitative assessment of school staff perspectives on the positive aspects and challenges of implementing the 17-week ACT program, an after-school intervention that integrated motivational and behavioral components to promote PA in underserved adolescents. Interviews were conducted with one school staff member from each participating school for all four trial cohorts (N = 12). Transcripts were coded by independent coders (r = 0.84) and content analyses of themes was performed using QSR NVivo. Themes were organized into five meta-themes: (1) Logistics; (2) Essential Elements; (3) Staff and Child Challenges; (4) Staff Comprehension, Value, and Enjoyment; (5) Spill-Over Effects. Findings indicate that staff can be successful at understanding, valuing, and reaching fidelity in implementing climate-based mediation components. The insight gained from this study lays the foundation for understanding the components needed for establishing well-implemented, effective, and generalizable interventions for increasing youth PA. (Contains 3 tables.)