The reasons for the mixed evidence of the effectiveness of school-based physical activity programs can be many, including implementation challenges. Studying program implementation can potentially contribute to enhancing effectiveness, the design of future interventions, improved implementation, and the interpretation of outcomes.For this process evaluation, individual interviews were conducted with 16 teachers who had implemented the program “Active All Year Round” in a fifth-grade school class (students aged 9–11 y) in 2017. Through systematic text condensation feasibility and barriers of program implementation, perceived program reach and the programs’ influence on social cohesion were identified and discussed.Teachers described the program as very feasible to implement and identified very few implementation barriers, the most prominent being time constrains. Perceived program reach was very high, and teachers reported that those students who are less confident when it comes to physical activity did not have differential participation than those feeling more confident about physical activity. Finally, the program was perceived to positively affect social cohesion in class.Active All Year Round is a standardized, flexible, and easily implemented program in Danish schools. Future studies are needed to study implementation from a student’s perspective and/or students’ role in and experiences with competition-based health programs.