Background: The problem of practice at Coronado Elementary School is the inconsistency of effective collaborative planning among the grade level teams. Purpose: This action research study aimed to determine teachers' perceptions of Professional Learning Communities and how they believed participation in a PLC impacts their professional development and classroom instruction in a Title I Elementary School. Literature Review: The purpose of the literature review was to examine information related to enhancing classroom instruction through the effective implementation of professional learning communities (PLCs). The researcher examined three themes for this literature review: (1) Professional Learning Communities, (2) Teacher Engagement, and (3) Data-Driven Decision Making. Research Design: Three questions guided the study--(1) How does an effective collaborative process among teachers in a Professional Learning Community impact teachers' perceptions of self-efficacy? (2) How does participation in a PLC impact teachers' instructional practices in the classroom? And (3) What does the action research team identify as the essential components of developing an active PLC in an urban, Title I elementary school? The researcher used an Action Research approach for the study to address the problem of practice. Data Collection and Analysis: The Action Research Team incorporated data collection methods to include personal interview questionnaires, focus group interviews, surveys, classroom and PLC observations, and personal journals. An analysis of the data revealed eight common themes that helped drive the analysis and understandings of the findings. Results: Through a thematic analysis of the data collection connected to the research questions, eight themes emerged from the data collected throughout the three action research cycles. The emerging themes were: Teacher collaboration, teacher efficacy, job-embedded learning, team accountability, data analysis, time, leadership support, and PLC structures. Conclusion: Based on the data collection and analysis, teachers perceived working in a PLC as beneficial to their self-efficacy and positively affecting teacher instructional practices. It will take school leaders to create the time and provide support to affect a PLC's efficiency positively. With limited time constraints and only working with one grade level, a more exclusive study of the PLC process will need to be conducted to support the research further. [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.]