The quality of school leadership is linked to student academic achievement (Leithwood et al., 2004; Thompson & Barnes, 2007; Glatthorn & Jailall, 1997; Lezotte, 1991; Edmonds, 1979; Hallinger & Heck, 1996; Crum & Sherman, 2008). The purpose of this study was to examine the instructional leadership (IL) of high school principals and its impact on student achievement, particularly in mathematics. This study sought to determine the: (1) self-perceived IL behaviors of high school principals; (2) IL strategies that influenced positive outcomes of academic achievement; and (3) relationship between the IL behaviors of principals and student mathematics achievement. Using a mixed methods approach, quantitative data was drawn from 26 principals who completed the Principal Instructional Management Rating Scale (PIMRS) survey (Hallinger, 1999) and qualitative data was gathered from three of these principals through an interview. Triangulation of data emphasized principal's impact on student achievement. Surveyed principals frame the school goals as well as supervise and evaluate instruction. Interviewed principals expressed the importance of: (1) shared IL functions; (2) teacher empowerment; (3) professional learning communities and other professional developments; (4) creating opportunities for all students to be successful; and (5) evolving the school culture. A positive correlation was found between principals' IL and student performance in secondary mathematics. Students have exhibited improved test scores in mathematics since the current instructional leader and principal began his or her tenure. This study begins to bridge the gap between principals' IL abilities and student learning outcomes, particularly in secondary mathematics. [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.]