This quantitative correlation survey study investigated the relationship between teachers' perceptions of the effectiveness of school principals as instructional leaders in professional learning communities (PLCs) and self-efficacy beliefs of teachers. Social Cognitive Theory, self-efficacy concept, and Adult Learning Theory were at the core of this research study design. Data was collected from 52 elementary classroom teachers from seven schools in an urban school district in Iowa. Two data collection tools were utilized to examine the research questions. The first tool was the Teacher Sense of Efficacy Scale created by Tschannen-Moran and Woolfolk Hoy (2001), and the second data collection tool was the Professional Learning Community Assessment-Revised developed by Olivier, Hipp, and Huffman (2010). Data was collected on teachers' perceptions of their own efficacy and their beliefs about their principals' effectiveness as instructional leaders in PLCs. Data analysis consisted of descriptive statistics and a series of Pearson correlation coefficients to analyze results of the survey and questionnaire. Results of the study indicate teachers who believe their principals are effective in facilitating PLCs have a higher sense of self-efficacy in the domain of Student Engagement. Also, teachers who reported a high sense of overall self-efficacy also believed in their principals' abilities to effectively create supportive conditions and structures for PLCs. Although a statistically significant relationship between collective efficacy beliefs and perceptions of principals' effectiveness as instructional leaders in PLCs did not exist, a strong and positive relationship was evident. [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.]