Teachers' engagement in school leadership is one of the most effective means of improving teaching and student learning. Given the complexities of facilitating instructional leadership tasks, school leaders can no longer fully streamline such tasks with fidelity. Therefore, including teachers' knowledge base and skillsets in school-based instructional leadership is crucial to helping school leaders improve instruction and student learning. York-Barr and Duke (2004) concurred in their teacher leadership study, sharing that the expertise of teachers is foundational for increasing teacher quality and advancements in teaching and learning. This qualitative research study explored how teachers' engagement in school-based instructional leadership initiatives influences self-efficacy and collective teacher efficacy (CTE). A teacher's self-efficacy is a teacher's belief in facilitating education behaviors using a unique skill set that will result in the desired outcome. CTE is the shared belief of teachers that their collective behaviors can result in the desired effect. Transformative learning theory was the backdrop of this qualitative study's interpretative phenomenological analysis. The study participants were eight school district teacher leaders serving low-performing Title I elementary schools in the southeastern United States. The research used open-ended questionnaires, semi-structured interviews, and focus groups to collect and analyze the data. The findings suggest the need for teacher leadership platforms at the school level and the parameters necessary for sustainability. [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.]