Principal leadership is one of the most heavily researched topics in the field of education and is a key to increasing school effectiveness and stimulating school change. One of the most important principal roles that have emerged in the literature is the facilitation of a collaborative culture. Teacher collaboration has been linked to a variety of positive outcomes such as improved instruction and student learning. Research indicates that collaboration is most effective when it is part of a district's professional development. Using a theory-driven approach, the present study evaluated a four-year collaboration initiative aimed to increase student learning in one Connecticut school district. More specifically, the study investigated whether principals' actions in support of teacher teams and the quality of teacher collaboration changed over time. Of particular interest was an examination of how principals influenced a collaborative shift in school culture and what specific strategies had the most impact on the quality of collaboration in teacher teams. Data were collected from a sample of 400 teachers, beginning in 2008 and ending in 2011, although sample sizes varied across time according to response rate. Items from the "Teacher Collaboration Survey" were used to measure teachers' perceptions of principals' actions in support of teacher teams and the quality of teacher collaboration. Hierarchical Linear Modeling (HLM) was utilized to measure change across time, accounting for repeated measures. No statistically significant changes were found for either principals' actions in support of teacher times or the quality of teacher collaboration. However, statistically significant correlations were found between these two variables in each of the four years, indicating a moderate to strong relationship. In addition, qualitative responses on the survey were used to investigate the high leverage behaviors that principals employed to create a cultural shift in this district and provided insight into the types of change that occurred during this initiative. Finally, implications and limitations of the present study were discussed, and future research in this area was suggested. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]