During 2019 the accreditation of a Catholic school serving students in special education, the Middle States Association of Colleges and Schools report recommended implementing a Positive Behavior Intervention Supports program (PBIS). This qualitative case study aimed to build on the growing research on Positive Behavior Intervention Supports and describe how it was implemented in a unique school setting. This study aimed to better understand the processes and practices of a School-Wide Positive Behavior Intervention Support program (SWPBIS) during the first year of implementation, gain special education teachers' perceptions and identify changes that have occurred through the implementation. Three main sources of data were collected through this study, including the Tiered Fidelity Inventory, an anonymous open-ended response survey, and various artifacts from the school to answer the research questions. Using qualitative inquiry, three major themes emerged highlighting the changes that occurred to the school culture: behavioral, social, and organizational changes. Findings from this study show that using a valid, reliable checklist as a tool to measure fidelity helps ensure the level of implementation. The findings also showed how professional development and support are needed for teachers when implementing new programs. This study discussed positive changes to the school culture that can occur when adopting a SWPBIS program. Future studies may explore how a SWPBIS is implemented in other Catholic special education schools. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]