This study was designed to analyze non-principal staff supervisors' perceptions of PLC efforts, encouragements, and activities in the six dimensions of a professional learning community (PLC) characterized as shared and supportive leadership, shared values and vision, collaborative culture, a focus on learning, supportive relationships, and supportive structures. By correlating that data with student achievement, this study sought to find which PLC dimensions and behaviors were associated with high student mastery, despite poverty. A survey was completed by 33 assistant principals and department chairpersons from selected high schools classified by New York State as suburban or small city districts. The NYS Comprehensive School Report Card demographic data was used to select schools with low-wealth. The schools were further stratified into two groups which had either the lowest or highest percentages of students who attained mastery level, averaged over two years, on the New York State 11th Grade English Language Arts Regents exam. The data showed that shared and supportive leadership was the strongest and only significant predictor of supervisor placement in lower or higher achievement low-wealth high schools among these New York State school districts.