A current trend in education is that small teacher groups, called professional learning communities (PLC), are being advocated as a tool to help teachers reach struggling students. Educators planning to use PLC as an intervention strategy can benefit from research-based information about PLC best practices. This multiple case study addressed the possible disparity between what is theoretically known of PLC as posited in the PLC literature and how these small teacher groups are functioning in schools. The study also explored how PLC might be improved to best serve students. PLC in 3 under performing senior high schools was examined. Research questions involved understanding how PLC operate in actual school settings, and how their functioning compared functioning described in the literature which emphasizes a collaborative cycle of inquiry to improve teacher practice. Principals, assistant principals, and teachers were interviewed. Each interview included open-ended questions about PLC implementation and functioning at the school site. Four PLC group meetings were observed by the researcher. Data were analyzed in 4 stages, including holistic analysis, categorical aggregation, cross case analysis, and comparative analysis. Results indicated that although teachers were generally positive about PLC as a professional learning forum, inconsistent implementation procedures can negatively impact PLC effectiveness. Strong administrative support and teacher familiarity with the goals and methods of PLC emerged as best practices. Recommendations include further autonomy for PLC and increased opportunities for teacher leadership. Social change will be brought about through improved student performance, especially in urban schools where test scores are critically low. [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.]