Group coaching is emerging as an approach with a strong potential for developing leadership competencies. However, there is little research on its use in the professional training of school leaders. In this study, we investigate the outcome of and the processes involved in group coaching using data from reflection papers and evaluations. The results suggest that group coaching fosters self-efficacy and promotes a clearer understanding of the school leaders' role. Moreover, the study suggests that theory from the field of psychotherapy can be a useful analytical tool for studying the processes that go on within group coaching.