This book consists the full study of the assessment of the factors affecting the effectiveness of principals' instructional leadership of public secondary schools of eastern city of Ethiopia, Dire Dawa. The success of educational organizations depend largely on the quality of its leadership. Effective principals motivate their subordinates to higher levels of productivity, remedy poor performance and lead schools towards their objectives. Instructional leadership is an unparalleled tool for principals to be effective in their endeavor to provide quality education to students. However, the exercise of instructional leadership is not a simple process that occurs without any difficulty. Many problems related to leadership functions of principals were observed from time to time influencing the school learning environment. The main intention of the study was to identify to what extent school principals are practicing dimensions of instructional leadership and the factors that affects the effectiveness of instructional leadership. The book includes background, literature review, research methodology, findings, conclusion and recommendation of the study.