Inappropriate behaviors are common during hallway transitions. Researchers have successfully reduced hallway transition times using the Timely Transitions Game, which involves applying interdependent group rewards delivered contingent upon a class's transition time. A multiple-baseline design was used to evaluate effects of a modified Timely Transitions Game (i.e., a response cost component was added to typical Timely Transition Game procedures) on inappropriate hallway transition behavior across three elementary summer program classrooms. Visual analysis of a repeated-measures graph and statistical analysis suggested that the modified Timely Transitions Game caused immediate, consistent, and meaningful reductions in inappropriate transition behaviors across classrooms. The modified Timely Transitions Game may be an effective prevention and remediation procedure consistent with approaches focusing on reducing inappropriate behavior via the application of behavioral strategies. Discussion is focused on the need for additional studies to evaluate longitudinal effects and the generalizability of the current findings.