Effective collaboration and the development of collective efficacy are understood to have considerable influence on students' learning, with research showing that the presence of collective efficacy among educators is the strategy with the most potential to positively affect student achievement. Yet this strategy is rarely found implemented in schools with any consistency. For teachers to develop collective efficacy there need to be conditions that support effective teacher collaboration in place. This means that site principals must be intentional in the way they design and support collaborative spaces for teachers, playing a key role in developing collective efficacy. The purpose of this case study was to examine and explain the influence a school site leader has on the development of collective efficacy and identify promising best practices principals should consider when approaching this work with their teacher teams. Principal interviews, a teacher survey, and a follow-up teacher focus group were used to explore the strategies being deployed at the sites studies and how they impact collective efficacy. The findings of this study suggest that principals need to intentionally design structures and designate resources for teacher collaboration like full-day sub-release time and consider campus composition and the proximity of members of an identified teacher team on campus. Principals should strive to strike a balance between administrative priorities and planning support with teacher-driven collaboration and the desire for autonomy, creating shared purpose for collaborative work. A structure identified through the study that helped to support leaders in implementing many of the identified practices and guide the work of developing collective efficacy in teacher teams was the Linked Learning approach. This approach provided externally validated standards for leaders to use in the design and purpose of team collaboration and appeared to be a driver at these sites. The findings of this study suggest that leaders should consider this approach as a potentially effective lever for developing collective efficacy in teacher 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.]