The World Health Organization ([WHO], 2018) encourages schools to engage with a multi-component, whole-of-school approach to physical activity promotion. However, little evidence exists describing the practices of schools that successfully promote a physically active school culture. The purpose of this study was to explore and describe the best practices of "active" secondary schools. Three schools, each in a different country (i.e. the United States, Finland, and Ireland), were identified as sites for investigation based on the presence of nationally established whole-of-school physical activity initiatives. Data were collected in one secondary school in each country and were generated from several sources including semi-structured interviews with stakeholders, field notes, three days of on-site observation, and artifact collection. Inductive analysis using open and axial coding was conducted (Corbin and Strauss, 2008). Three common themes related to best practices were evident at each site: an established school-based leader, support from the school community, and many available physical activity opportunities. Successful school-based physical activity promotion is possible if there is a motivated physical activity champion and if their promotion efforts are supported. These schools created multiple physical activity opportunities for students and have developed a strong physical activity culture.