This research focuses on the personal and professional characteristics leading to leadership development of school principals. It is consistent with the view that the principal's leadership is the cornerstone of any successful school (Barth, 1991). The principal is responsible for developing staff within the organization and their abilities (Senge 1990) while ensuring that their individual and collective contributions are put to work in the service of the educational mission. This approach is based on interaction, communication and shared listening. In this case, "The leader must know his team in terms of experience and potential as much as he must be known by his team" (St-Germain,2002, p.146). On the one hand, during his or her professional development, the school principal seeks advice and support from expert colleagues in order to carry out this mission. This form of support, known as mentoring, plays an important role "in the development of entrepreneurial self-efficacy"(St Jean & Mathieu, 2011, p.13). It is postulated that this form of support is also present in education. On the other hand, recent studies indicate that personal characteristics such as emotional competencies may be one of the most important elements of leadership (Goleman, Boyatzis & Mckee,2004). According to Anderson (2004), emotional competencies are considered "the most powerful force for improving school effectiveness and achieving excellence in education" (p.84). Few studies in education have examined the links between these three concepts: mentoring, emotional competencies and leadership. To our knowledge, no studies in the field of school management have examined the relationship between mentoring, emotional competencies and leadership style. In order to verify this relationship, a research review based on a systematic review of the literature on the links between mentoring, emotional competencies and leadership among school principals was first conducted. Second, the process of developing a questionnaire on the development of emotional competencies during mentoring was validated. Third, a path analysis was applied to explore the link between the three concepts under study. The results show that mentoring is an essential training instrument for the development of emotional competencies and that transformational leadership is the recommended style for an effective school.