The Good Behavior Game (GBG) is a universal prevention program designed to increase academic engagement and to decrease disruptive behavior in elementary school-age children. Teachers and other school personnel use interdependent group contingencies to improve students' behavior in the classroom. Previous research indicates the GBG is efficacious in reducing behavior problems; however, little research has examined its effects on academic achievement in real-world settings. In this study, the authors evaluated the PAX GBG, a commercially available version of the GBG, as it is typically administered in elementary schools. The authors examined standardized reading and mathematics scores across one academic year for 949 students enrolled in the GBG or comparison classrooms. Results showed significant but small effects of the GBG on reading and mathematics. Results were greatest for boys, children with lower achievement scores at baseline, and students from more economically disadvantaged school districts. School personnel may find the PAX GBG useful in improving children's behavior and academic skills.