Introduction In the last two decades, the world has witnessed the appearance of new theoretical models in the sphere of educational leadership. Two of the principal models, as evaluated by several empirical researchers, are instructional leadership and shared institutional leadership. In contrast to former leadership models employed by school administration (i.e. contingency theory, trait theories, and situational leadership), shared instructional leadership model lends credence explicitly on way in which educational leadership (employed by teacher and school administrators) leads to improvement in educational outcomes (Hallinger, 2003, p.329). Instructional Leadership: Definition According to Hallinger (2003), instructional leadership lends credence on the role of school administrator (principal) in organizing, running, directing and developing instruction and curriculum in the school (p.331). To put it in another way, instructional leadership emphasizes on the unitary function of the school principal. The instructional leadership model emphasizes on three critical role of school principal: defining the mission of the school; administering the instructional program, and supporting a positive learning culture (Hallinger, 2003, p.332). Southworth (2002) also defines instructional leadership as that which “assumes that critical focus for attention by leaders is the behavior of teachers as they engage in activities directly affecting the growth of student” (2002, p.73). He further classifies two variants: the narrow type, which confines its focus on the behaviors of teacher to improve student learning; and the broader one which lends credence to other organizational aspects. He also states that principals alone cannot execute all of school’s requirements for instructional leadership. What’s more, for instructional leaders to be effective, they must promote curriculum development, staff development and value a blend of supervision (Southworth, 2002, p.75). Emergence of Instructional Leadership Instructional leadership model first appeared in 1980s following numerous studies on successful school management practices. These studies identified “strong, directive leadership focused on curriculum and instruction from the principal” as an attribute of elementary school in deprived urban society (Hallinger, 2003, p.329). This leadership model influenced much of the thoughts on successful principal leadership publicized in early 1980s and 1990s globally. What’s more, instructional leadership was widely adopted by many principal leadership academies in the U.S. as the preferred model (Hallinger, 2003, p.330). Following the adoption of several school reforms in North America in the 1990s, practitioners and academicians started to give weight to terms such as transformational leadership, distributed leadership, teacher leadership, and shared leadership. The surfacing of these leadership models signaled a widespread displeasure with instructional leadership model. The discontentment with this model stemmed from the fact that it emphasized too much on the principal as the source of authority, power and knowledge (Hallinger, 2003, p.330). Evidence-Based Instructional Leadership The effectiveness of instructional leadership can also be gleaned from a study done by Blasé and Blasé. The study i