The purpose of this study was to investigate the perceptions of teachers on the effects of Positive Behavior Interventions and Supports (PBIS) implementation on their sense of efficacy in classroom management in a large urban district. Data was collected in two phases through an explanatory sequential design for mixed methods. Phase one of the study involved collection of quantitative data through discipline data and survey instruments. Discipline data showed differences in school suspension rates for students in PBIS schools in the district. The Teacher Sense of Efficacy Scale (TSES) from Tschannen-Moran and Hoy (2001) and the researcher’s PBIS and Classroom Management Efficacy Perception Survey (PBIS & CMEPS) were used to collect data on teacher perceptions. There was a positive correlation and a significant relationship between the results of the TSES and the PBIS & CMEPS. Phase two incorporated qualitative data collection through interviews with teachers from one Title I school in the district where PBIS was implemented, yet teachers and administrators were not able k maintain a downward trend in school suspensions throughout the years of PBIS implementation. Results of the study indicate the teachers in this district have a high sense of efficacy in classroom management and believe PBIS implementation has a positive effect on their efficacy in this area. Recommendations from this study include using stakeholder perceptions for continuous improvement of PBIS implementation that will lead to increased student achievement as a result of well-managed classroom behaviors of difficult students. Keyword 1: Classroom Management Keyword 2: PBIS Keyword 3: Positive Behavior Interventions and Support Keyword 4: Teacher Efficacy