In order for initiatives targeting physical activity in the school community to be effectively implemented, they need to 'make sense' from the school's perspective. That is, teachers need to see their value and feel confident that implementation will result in change. Teachers also need to feel competent in doing what's required of them to implement an initiative as intended. This study takes a mixed methods research approach (questionnaire and focus groups) to understand motivations, perceived benefits and challenges associated with implementing the 'Active School Flag' (ASF) initiative. Active School Flag 'coordinators' from Irish primary schools completed questionnaires (n = 236) and participated in focus groups (n = 19). Data were analysed using descriptive and Thematic Analysis (TA). Findings suggest that schools are both intrinsically motivated (e.g. 'to improve the health of the children') and extrinsically motivated (by recognition and status) to implement the ASF initiative. Results also reveal a litany of perceived benefits attributed to ASF implementation (including 'less active children become more active'). Conversely, results indicate that implementation comes with challenges relating to 'time' and 'paperwork'. Findings of this study have the potential to be used as inputs to improve the ASF implementation process and inform similar future programmes.