Campbell and Skinner used an A-B design to evaluate the effects of the Timely Transitions Game (TTG) on room-to-room transitions in a sixth-grade classroom. The TTG incorporated explicit timing, publicly posted feedback, and an interdependent group contingency with randomly selected transitions and criteria. The purpose of the current study was to use scientific procedures including (a) an experimental design, (b) interobserver agreement data, (c) treatment integrity data, and (d) procedural integrity data to validate the efficacy of a modified TTG on after lunch hallway-to-classroom transitions in an intact second-grade classroom. Across-phase comparisons of transition times revealed clear experimental control and suggest that the TTG caused decreases in transition times. Discussion focuses on empirical case studies, validating interventions, and using interdependent group reinforcement in a classroom setting.