This dissertation was designed to examine and assess teachers' perceptions of the effectiveness of Positive Behavior Interventions and Supports (PBIS) during virtual instruction resulting from the COVID-19 pandemic. The study examined whether teachers' race/ethnicity, years of teaching experience, level of education, and gender separately and taken together influenced their perceptions of effectiveness. The study took place at a middle school in northeast Georgia. The school in this case is in its third year of PBIS implementation. This study followed a QUAN-qual mixed methods case study approach in the collection and analysis of data to develop conclusions of teachers' perceptions of the effectiveness of PBIS during virtual instruction. Quantitative data were collected through a survey created by the researcher for teachers. Qualitative data were collected through semi-structured interviews. By combining quantitative and qualitative data, the researcher was able to provide a better understanding of teacher ratings of effectiveness at the selected site. [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.]