In July 2017, the state of Georgia implemented a teacher certification renewal program that required educators to participate in a job-embedded professional learning communities (PLCs) facilitated by local school districts. This study investigated the shared instructional leadership behaviors and teacher collaboration found in effective PLCs in one high-needs high school in Georgia. The administrators of the high-needs high school selected for the study, point to the work of their established PLCs as being responsible for a 16% increase in graduation rates over a 3-year period. This inquiry used quantitative data from the Teacher Collaboration Assessment Rubric (TCAR; Woodland, 2016), which assesses 15 content-specific PLCs and data collected from a Likert scale teacher questionnaire. The TCAR and teacher questionnaire quantitatively assess each PLC by looking at four categories of collaboration: dialogue, decision making, action, and evaluation. The study used the principles of shared instructional leadership to investigate the behaviors that are prominent in established PLCs. A multiple regression analysis was used to predict the effectiveness of PLCs based on teacher collaboration as measured by the teacher questionnaire. Along with addressing a void in the literature regarding high school PLCs, this study provides a perspective on a state-mandated change to professional development. The results demonstrate that teacher collaboration has a statistically significant impact on predicting effective PLCs in a high-needs high school.