This study focused on leadership effectiveness of high school principals within the New York City Department of Education. The purpose of this study was to explore the views and perspectives of teachers concerning the impact of principals' leadership style on teachers' and students' performance and to determine teachers' perceptions of the leadership styles adopted by their principals and if they feel supported by their principals. This study also sought to establish whether teachers have a personal relationship with their principals, and if so, how this influences their perspective of the leadership style adopted by their principals. Moreover, does a principal's perception of their leadership style align to their teachers' opinion of their leadership style? This study was conducted using a qualitative approach where purposive sampling technique was used to select 15 high school teachers and 5 high school principals. The data came from surveys and semi-structured interviews, which were conducted via telephone and online. The results show that principal leadership enhances teacher's performance by providing them with professional development opportunities and promotion of collaborative working. The majority of the teachers strongly agree that the leadership style of a principal does affect teacher performance. The majority of the teachers in this study have a positive perception of the leadership styles adopted by their principal. They assert that a personal relationship with their principal enhances their perception of leadership style because the relationship eliminates barriers between teachers and their principal, thus enhancing the effectiveness of the leaders and teachers' performance. However, this type of relationship does not seem to influence how teachers perceive their principals' leadership styles. Moreover, a principal's perception of their own leadership style does not align with the teachers' opinion of their principal's leadership style. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]