Multicomponent, community-based programs aiming to improve health behaviors in youth are needed but can be challenging to implement. Research is needed to better understand the factors that facilitate and inhibit effective implementation of these programs especially for youth at increased risk of health disparities. This study aimed to identify and explore the implementation determinants and outcomes of a multicomponent health intervention conducted from 2021 to 2022 for middle school students living in underserved communities in Philadelphia, PA, USA. Mixed methods approaches, including self-report surveys and semi-structured qualitative interviews, were administered to 18 members of the implementation staff at the end of the program, including coaches (n = 7), assistant coaches (n = 2), school champions (n = 6), administrative leaders (n = 2), and a school district administrator (n = 1). Survey and interview questions were guided by the Consolidated Framework for Implementation Research (CFIR), and interviews were thematically coded following transcription based on 26 CFIR constructs. Innovation source, evidence strength and quality, cosmopolitanism, and the personal attributes of individuals were key constructs associated with implementation effectiveness. Data revealed three multidimensional themes that highlighted broader challenges influencing implementation: (i) broad consensus, different interpretations, (ii) staffing challenges, and (iii) continuity is key. The need for the program was clearly recognized and overall belief in the purpose of the intervention was strong among key program staff and administration. However, issues including limited engagement with training, staffing turnover, and the rotational programming design hindered implementation. Future projects aiming to implement multicomponent after-school time interventions must ensure a consistent vision among partners and continuity in program delivery.