The issues arising from the intensification of international mobility can be seen at many schools and generate daily challenges. However, many studies highlight the lack of training for principals on the realities of environments with diversified school populations. In the wake of these findings, we conducted an action research/course on transformative leadership in multi-ethnic Montreal with six school principals. In this article, we discuss the process for the project, and its theoretical anchors in transformative leadership (Shields, 2010) and the inclusive education model (Potvin, 2014). We then present a thematic analysis of interviews conducted with elementary school principals at the end of the three-year project to determine the perceived effects of this initiative on their professional practice - on their leadership, knowledge and know-how. It shows that principals have developed a critical awareness of themselves, their environment and society, and have implemented equity and inclusion practices in their schools. In conclusion, we provide avenues for improving initial training for principals and their skills base in Quebec.