Transitioning from elementary to middle school is a time of particular vulnerability for students with behavior problems. This study examined the effects of class-wide function-related intervention teams (CW-FIT) in three middle school classrooms to determine whether this multitiered intervention could help teachers proactively manage student behavior. With a focus on teaching classroom expectations, delivering behavior-specific praise, and providing differential reinforcement within an interdependent group contingency, CW-FIT is designed to teach functional replacement behaviors that support students' academic engagement. Intervention effects were assessed with seventh- and eighth-grade students from diverse backgrounds. Results, evaluated using a single-subject withdrawal (ABAB) design, indicated improved rates of on-task behavior at both class-wide and individual student levels, with corresponding increases in teacher praise and decreases in teacher reprimands. The positive way in which participants viewed CW-FIT implementation and its accompanying effects on student behaviors was consistent with earlier findings in elementary schools. Study limitations and areas for future research are discussed. [For the corresponding grantee submission, see ED616822.]