The school principal has a specific role in the school environment, which for the most part is bureaucratic. However, given the constantly changing environment in which the school operates and given the relationship between the school and the local community, the school principal needs to undertake additional responsibilities and moreover also possess specific skills in order to fulfil his or her role as a principal-leader. The ultimate research goal is to determine the purpose of leadership within the school unit. The method adopted for the study was a review of the relevant literature. In light of the present study, it is evident that in order for educational organizations, or otherwise educational units, to accomplish their purpose, effective management is a prerequisite. As regards the factors that contribute to school effectiveness, researches have shown that there is an inseparable link between school unit leadership and school effectiveness. An effective school principal-leader assists and supports teachers, while overseeing the educational work, and also encourages and promotes the involvement of teachers and parents in the decision-making process, which leads to the commitment of teachers to the school organization and increases their job satisfaction and performance. Furthermore, teachers should be able to teach all children, both those with high cognitive abilities and those with a low level of academic skills. An important role in this process plays the principal of the school. However, teachers, on the other hand, should not simply accept the principal’s vision, especially if they want to be an integral part of the process of school change. Instead, teachers should create a vision for the school together with the principal, and not just act as executors of his/her vision. Finally, four factors characterize the successful process of improving the school unit. These factors are: recognition of the improvement process by the school leadership, interaction and communication both between school members and between the school unit and the local community, the existence of a system of values, as well as cooperation between school members, and between them and society, to design and implement the selected strategies.