The efficacy of the Good Behavior Game was examined in a multiethnic New York City public high school. Classroom rules were posted and students were divided into two teams. A reinforcement preference questionnaire was used to select daily and weekly prizes. The classroom teacher indicated that he was going to place a check on the board after every rule infraction as he named rule violators and their infractions. Students were also told that the team with the fewest marks at the end of each day would become the daily winners and receive prizes. They were also told that the team with the fewest marks for the week would be recognized as the weekly winners and receive additional prizes. The rate of disruptive behavior was charted across four treatment phases using a reversal design. The game phases were associated with marked reductions in the rate of seat leaving, talking without permission, and aggression. Teacher and student feedback supported the social validity of the procedure.