Especially, Marks and Printy (2003)[9] have pointed out the importance of the collaboration between principals and teachers to develop curriculum and instruction for improving pupils' performance. Thus, they conceptualized this inclusive approach as “shared instructional leadership” and understood the role of principals as that of “leaders of instructional leaders”. Hallinger (2003)[3] has argued the transformational leadership approach, in which leadership is shared with school staff; this approach is said to empower staff.