Students who disrupt the classroom due to externalizing behaviors can impact all of these, but more importantly, these behaviors interrupt student learning. Due to these stressors, the purpose of this study was to explore how a behavior intervention program, Class-Wide Function-related Intervention Teams (CW-FIT), within the scope of teacher professional development, can impact students' behaviors, improve teacher retention, and ultimately improve academic experiences in a suburban elementary school in Southwest Missouri. The mixed-methods study used a convergent mixed method design to explore how the CW-FIT impacted behaviors of elementary students. It also examined the correlation, if any, between teacher professional development of the CW-FIT and office referrals, teacher retention, and student achievement. Participants in this research study started with 12 elementary teachers and 10 classrooms. After the Pandemic began, the study continued in the fall of 2020 and included 11 teachers and nine classrooms (from third to fifth grade). Analysis of observation results, documents, and interviews, found that CW-FIT positively impacted student behavior in the participating elementary classrooms. Evidence showed the need for PD, how the CW-FIT increased student achievement through student engagement and teacher praise, and on-task behavior. [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.]