When students display disruptive behaviors, it interferes with their own, and other students' learning and with the teacher's ability to instruct during academic activities. This study investigated the effects of a classwide interdependent group contingency on the on/off-task behaviors of an at-risk student in a first-grade classroom in a private Midwestern school. The student was referred for intervention due to his high rates of off-task behavior and low levels of academic engagement. An ABAB withdrawal design was used to evaluate the effectiveness of the intervention to improve the target student's behavior as well as that of his classroom peers. Results suggested that the intervention decreased the individual student's off-task behavior and increased academic engagement while also having positive effects on overall behavior in the classroom.