The purpose of this study was to identify factors associated with Danish schoolteachers sustained use of classroom-based physical activity and to point out usable ways to support teachers in their professional practice. The study reports on data from in-depth interviews with nine teachers across grade levels and subjects. Supportive elements influencing sustained use of CBPA were: didactical skills; teacher collaboration (including sharing and co-creation of activities); and resources focusing on suitable physical activities. This study underlines that integration of classroom-based physical activity is a reflective teaching practice, and that activities are not just an addition, but something that has to make sense for the content of subjects, for the students and for the individual teacher.