A wide body of literature has documented the disproportionality in exclusionary discipline rates (Gregory et al., 2010; Losen et al., 2015; Office of Special Education Programs, 2020; Skiba, 2014; Welsh & Little, 2018). Students with disabilities or other minority backgrounds are removed from their classrooms at higher rates than their peers (Losen & Gillespie, 2012; Office of Special Education Programs, 2020). Such punitive practices have been associated with negative outcomes for the most at-risk youth. Thus, educational stakeholders have begun to move away from these punitive practices toward more positive behavior management methods. This study sought to examine the impact of an evidence-based classroom management intervention, known as CW-FIT MS, on student and teacher behavior in inclusive secondary classrooms, including the intervention's impact on teacher-student relationships and academic outcomes. Specifically, the intervention's effectiveness on improving student appropriately engaged behavior--particularly for individual students identified as exhibiting high rates of unwanted behavior. This study also evaluated the effectiveness of the intervention on improving teacher rates of behavior specific praise statements and decreasing their use of reprimands. Another primary goal of this study was to enhance our understanding of social validity and the specific components of CW-FIT teachers found themselves continuing to use after the study ended. Teachers and students were recruited to participate from a high school with a small number of students from diverse ethnic or minority backgrounds and low socioeconomic status. Two classrooms participated in the study, one at the 11th grade level and one at the 12th grade level. Both classrooms were taught by one teacher, with no co-teacher present, in general education settings where the state-mandated regular curriculum standards were being taught in English Language Arts. Both teachers were trained in implementing the CW-FIT MS intervention in their classroom. A single case withdrawal (ABAB) design was used to evaluate the intervention's effects on student and teacher behavior. The results of the study found a functional relation between the intervention implementation and increased appropriately engaged behavior for all students, including those who were rated as exhibiting high rates of unwanted behavior prior to the intervention. Also, the findings include increases in the teachers' use of behavior-specific praise statements and decreases in the use of reprimand statements. Other findings of this study were improvements in academic achievement and teacher-student relationships following the intervention. Finally, social validity aspects of the intervention were evaluated using surveys of both teachers and students to understand participants' perceptions of and satisfaction with the intervention. Results indicated students found the intervention favorable, but teachers' perceptions were less favorable. [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.]