Problem: Professional learning communities (PLCs) are not a new trend in education but are getting more attention in schools today as a vehicle for establishing collegial relationships among teachers and for building capacity for change within schools (Dufour & Eaker, 1998; Fullan, 2004; Hord, 2004; Senge, 2000). Schools are working diligently to become PLCs in hopes of improving student learning yet there are pitfalls schools must be cognizant of. The core principles of PLCs do not simply exist because leaders are calling them PLCs. Dufour cautioned "the term has been used so ubiquitously that it is in danger of losing all meaning" (Dufour, 2004, p. 6) while others warned of contrived collegiality as opposed to genuine collaborative teacher cultures (Hargreaves & Dawe, 1990). This study explores the development of PLCs at one middle school to provide feedback to improve practice while also building the research base on what contextual factors contributed to PLCs and how PLCs impact key components including pedagogy and assessment. Research Questions: The questions explored in this case study of one grade level in a middle school are: 1. In what ways does teaching practice change as a result of participation in a professional learning community? 2. What aspects about the PLCs contributed to the change? 3. What contextual factors contributed to the PLCs capacity to support teacher change? Methodology: A qualitative case study was used focusing on information gained from interviews, observations, surveys, and documentation for this study. The administrative team and core eighth grade teachers were interviewed and 4 observations of PLC meetings were completed. Data analysis included organizing and analyzing data using Dedoose, a qualitative research software program. Significance: Research on PLCs has typically focused on understanding what true PLCs are and how they can improve schools. This study focuses on identifying what types of changes took place in terms of pedagogy and assessment as a result of participating in PLCs. In addition, by focusing on a school that began the implementation process five years ago, the study aims to identify aspects about PLCs that contributed to instructional change. The study also identifies contextual factors that were critical for PLCs to support teacher change in order to help other school leaders that may be initiating PLCs in their own schools. [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.]