The study examined the perceptions of school leaders in developing collective efficacy and the ways in which they enact leadership to advance or impede the professional learning communities' ability to produce the intended results. A mixed-method case study at a public unified school district in southern California was conducted, which included principals at all secondary schools completing an online survey and interview. The purpose of the study was to understand the role of leadership in developing collective efficacy in professional learning communities. The need for colleagues to work together and to be a team is what motivates members, along with providing the necessary time to collaborate during their work day (Fullan, 2005). All nine participants agreed with Bandura (1993) and believed that collaboration is a prime factor that impacts collective efficacy in PLCs. The research findings revealed that collective efficacy was predicated on building trust, aligning resources, collaboration, and enhancing confidence through professional development. In addition, a hindering was teachers have a difficult time analyzing and sharing student data with members of their professional learning communities. This study begins to identify how administrative leadership is a highly important factor in fostering collective efficacy within a school staff. [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.]