Professional Learning Communities (PLCs) are being used as a form of teacher professional development in schools across the world. The concept has been present in the educational literature for over thirty years. While many educators are familiar with the term, some schools have not yet implemented PLCs. Hord (1997) determined that all true PLCs contain the following elements: supportive and shared leadership, collective creativity, shared vision and values, supportive conditions, and shared personal practice. This study examined the current use of PLCs in Pennsylvania public high schools through survey research of teachers. 171 high schools were randomly sampled to participate in this study and teachers from three of those schools participated in an online survey. Survey data was used to determine teachers' perception of PLC implementation of PLCs in their high schools. Additional items were added to the instrument to measure teachers' ratings of PLC effectiveness. Spearman's Rank Order Correlation was calculated and a positive correlation was found between teachers' classifications of PLC implementation and teachers' ratings of PLC effectiveness. A statistical analysis comparing teachers' classifications of PLC implementation to student achievement, as well as comparing teachers' ratings of PLC effectiveness and student achievement could not be conducted due to the size of the sample. A limited sample size prevented the researcher from rejecting or accepting the null hypotheses. However, preliminary comparisons suggest that there may be a relationship between PLC implementation and student achievement. Additionally, it appears that a relationship may exist between teachers' perceptions of PLC effectiveness and student achievement. Further research would need to be done in both areas to validate these claims. The researcher was also able to compare date from schools that used PLCs to those that did not use PLCs. Comparisons within the city locale type were not possible as only one city school responded. The rural school that used PLCs had the highest student achievement of all rural schools who responded to the researcher's request to participate in the study. The suburban school where PLCs were used also had the highest student achievement scores of all suburban schools who responded to the study request. The town school that used PLCs had the lowest mathematics and reading proficiency of all town schools that responded; this school did have the second-highest graduation rate of the group. The researcher makes suggestions for future research that include a case study, the use of a larger sample size, improvements to the participant strategy, modifications to the methodology, and a new study that would investigate the type of professional development used across the state. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]