Educators are continuously confronted with initiatives to increase student achievement; however, teacher isolation may hinder advancements to improve student learning. Teacher isolation may be a problem at many schools in which student achievement is not progressing, and teachers are not sharing pedagogical knowledge or instructional practices. Professional learning communities (PLCs) are designed to limit teacher isolation by increasing teacher effectiveness and student achievement through collaborative cultures. The purpose of this qualitative case study was to describe and investigate teacher interpretations of PLCs. The research questions addressed how PLCs impact teacher knowledge, teacher practices, and student achievement, as well as how principals and teachers sustain PLCs. The theoretical framework for this study was influenced by Knowles' andragogical learning theory and PLC researchers Blankstein, DuFour, Hord, who investigated the benefits of PLCs in regards to student success and overall school improvement. Data were collected from eleven participants through interviews, a focus group, and a teacher self-evaluation. Rubin and Rubin's data coding and analytic protocol for interpreting interview data was used to analyze the data. The findings indicated that the participants interpret PLCs as a collaborative culture that is conducive for teacher learning and student achievement. This study contributes to positive social change by increasing teacher awareness and understanding of how collaborative cultures, specifically PLCs, contribute to overall school success. [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.]