This study is an examination of the effectiveness of the Mystery Motivator--an interdependent group contingency, variable-ratio, classwide intervention--as a tool for reducing disruptive classroom behavior in eight diverse general-education elementary school classrooms across seven different schools. The study was conducted using an ABAB, changing criterion design, and the effectiveness of the intervention was assessed for an 8-week period. The frequency of disruptive behavior in all classrooms decreased. Teacher intervention acceptability data indicated seven of eight teachers found the intervention to be acceptable. Overall, data indicated the Mystery Motivator intervention was a powerful intervention for reducing disruptive behaviors in elementary classrooms.