The purpose of this study was to explore specific leadership practices of high school principals, as identified by teachers and principals, and these practices' relationship to student achievement in English language arts. The measurements used for student achievement in English language arts were the proficiency percentages on the 2016 New York State Common Core English Language Arts (NYSCCELA) Regents examination. The participants in this study were 12 principals from Long Island, New York and 22 teachers distributed among these 12 high schools. Research on leadership practices in various organizations, including schools, has been conducted using the "Leadership Practices Inventory" which is comprised of a self-reporting tool for the leader, and an observer tool for those with whom the leaders works (Kouzes & Posner, 1988, 2002, 2013) . This tool is grounded in a framework for leadership that identifies five critical competencies expressed by leadership practices. These five leadership practices are "model the way," "inspire a shared vision," "challenge the process," "enable others to act," and "encourage the heart." A quantitative methodology was used in this study and data used included survey responses of principals and teachers, along with achievement results from each high school on the 2016 NYSCCELA Regents examination. A strong and significant correlation was indicated between proficiency percent and the leadership practice of "model the way." In addition, correlations were found among the five leadership practices indicating the tool was effective. Finally, significant effects were found in two cases, specifically with regard to the impact of "challenge the process" and "enable others" on the outcome of proficiency percent. Implications for principal preparation programs and ongoing principal professional development appear to be evident. One of the recommendations for further research is to conduct a study with a larger sample size in order to determine if similar findings are revealed in order to generalize findings. Another recommendation is to return to the participating schools to conduct interviews with the principals in order to identify specific actions in which they engage and assign them to one of the five leadership practices. Categorizing specific actions of a principal may reveal certain themes that could inform leadership practices. [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.]