During the transition from elementary to middle school, adolescents may become increasingly vulnerable for emotional and behavioral problems. Class-Wide Function-Related Intervention Teams for middle school (CW-FIT MS), the independent variable examined in this study, was developed to improve teaching and learning by fostering student engagement. The study's purpose was to examine the feasibility and effects of CW-FIT MS Tier 1 implementation across nine middle school classes using a single-subject ABAB withdrawal design. Participants were 234 students in grades 6-8, including 23 identified as at risk for emotional behavioral disorders. Results of CW-FIT MS Tier 1 implementation showed significant improvement in on-task behavior for groups as well as individual target students, increased teacher praise-to-reprimand ratios, and decreased target student disruptions. Outcomes of social validity surveys were consistent with earlier studies. Study findings extend previous results by demonstrating positive intervention effects in novel settings with a greater number of participants. Study limitations and areas for future research are discussed. [This paper was published in "Research in Middle Level Education" v42 n7 p1-15 2019 (EJ1226018).]