Urban high school achievement gaps persist despite efforts by principals and extensive research on the positive role of Collective Teacher Efficacy (CTE), signaling the need for additional support. This study investigated the potential of teacher leadership in fostering CTE within large urban high schools. Using a mixed-methods multiple case study design, it identified essential characteristics and skills for enhancing CTE. An important goal included informing training initiatives in supporting teacher leaders to enhance their teams' CTE. Employing an explanatory sequential design, the study utilized surveys to establish CTE mean scores and then conducted interviews with four teams. Key themes emerged, emphasizing teacher leaders' responsiveness to teacher needs, building community and relationships, prioritizing collaboration, and influencing and advocating for their teams. Critical teacher leader attributes included being strategic, approachable and flexible, and organized. External factors influencing teacher leadership were identified, underscoring the importance of administrative support, and highlighting hindrance factors such as top-down mandates and low time for collaboration. The findings provide valuable insights into the complex interplay between teacher leadership and CTE, providing implications for education leaders. The results also underscore the need for targeted training for teacher leadership, emphasizing addressing gaps in formal training, providing strategies for collaborative teams, and developing conflict resolution skills. [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.]