The concern about problematic, disruptive student behavior, declining academics, and their relationships at an inner-city elementary school in the southeast United States had persisted despite positive behavior interventions and supports (PBIS) implementation for two years. The purpose of this basic interpretive qualitative study was to explore teachers' perceptions of their effectiveness in implementing PBIS in their classrooms, and how PBIS affected teachers' self-efficacy. Power's perceptual control theory, the PBIS framework, and Baer, Wolf, and Risley's applied behavior analysis served as the theoretical frameworks to guide this study. Specifically, this study explored how teachers in this elementary school perceived their ability to implement PBIS in their classrooms and how teachers in this elementary school perceived how implementing PBIS in their classrooms affected their teacher self-efficacy. The study included interviews, field notes, and survey data from 15 purposefully selected teachers from kindergarten through sixth grades who were known to meet the selection criteria of teachers who taught at the study school for one school year prior to this current research using the PBIS framework. Data were analyzed using Braun and Clarke's six steps of thematic coding. Findings indicated that teachers felt comfortable and confident teaching PBIS; a lack of teacher PBIS training for implementing the framework; and a lack of school-wide attainment and teacher buy-in. Themes supporting the findings included that teachers supported PBIS implementation, but more training was necessary to achieve program fidelity. Further research is recommended exploring how the PBIS leadership team prepares teachers for PBIS program implementation and how teachers are trained to provide additional supports for tier two and three students. The implications for reform efforts are dependent on teachers' abilities to effectively implement PBIS in their efforts in improving student conduct within the school. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]