Background: Physical inactivity has been identified as the fourth leading risk factor for global mortality. Despite public health guidelines advising children and adolescents to spend a minimum of 60 minutes per day of at least moderate intensity physical activity, a large proportion of children and adolescents fail to meet these guidelines. Interventions promoting physical activity show varying degrees of success, and more detailed evaluations of such interventions are essential. The aim of this research was to conduct an in-depth evaluation of a community-based physical activity program aimed at children and adolescents, specifically the Tribe Project. Methods: The RE-AIM framework (Reach, Effectiveness, Adoption, Implementation and Maintenance) was used to evaluate the individual and organisational-level impact of the Tribe Project. A single mixed method case study was used based on five sources of evidence: interviews, questionnaires, documentation, archival records and direct observations. Participants included the Tribe managers and coaches implementing the program and the Tribe parents and children/adolescents who attended. Results: The Tribe Project reached approximately 2.5% of the eligible population living within Bath and North East Somerset. The program successfully met some of its objectives although feedback procedures were poor and the program aims were unclear. The community-level adoption of the program was high, however, the implementation and adherence to the program principles at the setting-level varied. The program was successfully institutionalised within the University of Bath yet pathways after the program into the community varied, and were mostly competitive only. Nonetheless, a combination of social, psychological and physical benefits was reported following participation. Conclusion: To assess accurately the potential impact of physical activity interventions a combined assessment of individual and organisational-level factors is necessary. This will help inform policy on effective strategies to promote physical activity in the community, and develop interventions that are more effective as a result.