Professional Learning Communities (PLC's) are designed to help schools improve student achievement; all decisions are based on the needs of students. PLC's are an effective way to receive professional development (PD), allow for collaboration with fellow teachers, and offer timely intervention to all students. In a district known for PLC implementation, this study investigated teachers' perceptions about student achievement and their participation in PLC's. Using a mixed method approach, the research explored whether teachers believed their participation in PLC's led to increased student achievement at their schools and whether value-added data supported their perceptions. The District Climate Survey (DCS) was distributed to all district secondary teachers in May 2012 and evaluated which schools implemented PLC's most effectively. API (Academic Performance Indicator) data for 2008-2012 was analyzed to determine which schools performed above or below similar schools and how the schools compared to each other. The DCS data was compared with the similar school data to see if there was a difference in the responses of teachers at schools that performed above or below similar schools. The analysis determined that schools where teachers rated the PLC climate higher on the DCS also were schools that performed above similar schools. The Teachers' Perceptions about Student Achievement Survey (TPSAS) was administered to teachers at the selected six secondary schools during August 2012. The TPSAS determined what teachers believed was the cause of increased student achievement at their school sites. The data was analyzed by both individual school site and whether the school performed below or above similar schools based on API data. The analysis determined that teachers identified more PLC characteristics as the reason their schools experienced increased student achievement at schools that performed above their similar schools. These results indicate that PLC's can indeed transform schools. Schools that saw the largest API growth, compared to similar schools, cited being responsive to individual student needs as one of the most common reasons for increased student achievement. All secondary schools in this district have implemented PLC's and all have seen increased student achievement. [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.]