This study sought to compare teacher participation in a Professional Learning Community with the performance of their students. Student achievement data from multiple subject-alike groups were compared in a pre-and post-PLC format, using an independent, two-sample t-test. Overall, 10 PLCs from one high school in a suburban, Iowa setting were compared. Mean scores from the 3 research questions that guided this study found that (1) 7 of the 10 PLCs improved student learning after functioning as a PLC, (2) no consistent relationship existed between teacher participation in a PLC and student failure rates, and (3) no consistent correlation existed between the student learning results from effective PLCs (as measured by the Aylsworth PLC Survey) and those that did not meet the criteria of an effective PLC. Based on the findings of this study, implications for educational practice and suggestions for future research include (1) collaboratively setting the vision for PLCs, (2) researching and understanding the implementation and structures of PLCs, (3) providing appropriate resources and ongoing support for PLCs, and (4) developing supportive leadership for PLCs. [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.]