Several researchers have outlined the characteristics and components of instructional leadership. Hallinger and Murphy's (1985)[1] conceptual model has been most widely used in empirical studies of instructional leadership.[2][3] The authors proposed the key role of instructional leaders in three dimensions: 1) Defining the school mission, 2) Managing the instructional program, and 3) Promoting a positive school-learning climate. In these three dimensions, principals have different functions.