Through the years, the role of the school principal has shifted from managerial to an instructional focus, which required additional skills, strategies, oversight, and flexibility. Assuming the role of instructional leader challenged principals to ensure students achieve at high levels. Legislation over the years added to the high expectations with a focus on data and school improvement. The impact of the principals in the highest achieving secondary schools in Ohio was examined related to adapting leadership styles to developmental needs of staff. The concept of instructional leadership within the framework of situational leadership was analyzed through the case study method with semi structured interviews of 10 principals in the top 1% of Ohio public secondary schools. Principals were selected based on the performance index achievement score of their schools and asked questions related to instructional leadership and Situational Leadership® theory. Thematic analysis focused on the four quadrants of the SLII® and instructional leadership behaviors and practices. Similarities and differences were extracted and studied through the lenses of instructional and Situational Leadership®. Recommendations for current practitioners were made based on common themes discovered through the interviews. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]