Understanding factors that influence children's participation in sport and physical activity is critical to designing more appealing youth opportunities and programmes. Whole-of-school initiatives offer one way to promote children's physical activity, but little is understood about how celebration within these initiatives influences children's physical activity behaviours. Through this study we aimed to answer the question: what are participants' experiences of physical activity-related celebration within a whole-of-school physical activity initiative? Answering this question helped us to explore the relationship between celebration and school-based physical activity participation. This study was situated within Irish primary schools (N = 14) who were working towards the award of an 'Active School Flag'. Data for analysis included each school's Active School Flag application (N = 14), individual interviews with Active School Flag coordinator teachers (N = 14) and focus groups (N = 13) with children (N = 62). An inductive approach to analysis using open, axial and selective coding was employed. Celebration was an important part of the Active School Flag process, and the messages children associated with celebration were influential in shaping their understanding of what was important in relation to their physical activity participation. Acknowledgement of the merits of competitive sport beyond the focus on winning led to more inclusive physical activity approaches. Messages indicating that effort and participation were valued alongside excellence and winning were an important source for children to consider when making judgements about physical activity participation. Findings indicate the merit of including physical activity-related celebration within whole-of-school physical activity initiatives.