Since the No Child Left Behind (NCLB) era many program improvement schools were prescribed Professional Learning Communities (PLC) professional development as a corrective action by their respective Local Education Agency (LEA). Despite the adoption and implementation of many corrective action measures (including PLCs) recommended by LEA’s, the achievement gap persists in the majority high school campuses nationwide. Millions of dollars have been invested in the PLC method of collaboration with little systematic success in closing the achievement gap in standardized test scores, A – G requirements and college admission. There may be plenty of other factors contributing to the lack of improvement (i.e. instruction, grading practices, assessment of learning, interventions, attendance, student discipline, etc.) – but to what degree is the investment in Professional Learning Communities contributing (or not contributing) to this? Dufour & Eaker (1998, 2003, 2008) argue that schools with PLCs that are not improving student achievement is attributed to them not implementing the prescribed methodology with fidelity. However, could there be other reasons? A review of the literature identified gaps in the research that could provide other reasons: objective assessment of PLCs, as well as PLC autonomy and PLC trust. This cross - case study used a sequential explanatory mixed-methods design (Creswell, 2013) to analyze teacher perceptions of PLC fidelity, PLC autonomy and trust from two school sites in San Diego with similar student demographics, from the same school district, but with different trending student achievement results. Survey, interview, and field observation findings from this study suggested that Bayside High School and Parkview High School have similar PLC procedures, logistics and generally follow the Dufour & Eaker (1998; 2004) PLC model with fidelity. However, the findings also suggested that PLCs at Bayside High School have more autonomy and trust than PLCs at Parkview High School. The difference in PLC autonomy and trust could be one explanation for the difference in student performance. Additional findings also suggested that internal relationships, motivation, and vulnerability factors could be impacting PLC performance and student achievement at both sites.