American schools are complex organizations responsible for the teaching and learning of students. Leading these dynamic institutions is the school principal and the influence of the principal is a leading factor in school outcomes and student achievement measures (Grissom et al., 2021). Thus, the principal is essential for school and student success; however, the complexity of secondary schools combined with increasing demands for accountability and school reform initiatives requires a collective approach to school leadership. As a result, the number of assistant principals has significantly increased to provide support and assistance in the leading and management of the school. The administrative team, acting on behalf of the principal, is instrumental when measuring school effectiveness and despite the prevalence of administrative teams, the research literature is largely silent on the collaborative structure responsible for school leadership. Moreover, there remains little investigation exploring the leadership styles of principals, the organization of administrative teams, and the perception of team effectiveness by the principal. This explanatory sequential mixed-method study explored this unknown landscape by delving into high school principals' perceptions of essential factors for high-performing administrative teams. As such, this study addressed the following research questions: 1) How do high school principals describe their leadership styles? 2) How do high school principals organize their administrative teams? 3) What essential factors do high school principals feel contribute to the effectiveness of their administrative teams? Three literature streams provide contextual understanding, and the streams are: 1) The Principalship, 2) School Leadership Models, and 3) Effective Teams. [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.]