Interventions that target on-task behavior are essential, as on-task behavior is linked to the amount of learning that occurs in a classroom. "On-Task in a Box" is a manualized intervention to increase on-task behavior that utilizes video modeling and self-monitoring in conjunction with group contingencies. The current study evaluated the effects of the "On-Task in a Box" intervention on student on-task behavior and work completion when implemented as a classwide intervention. A multiple probe design across three elementary classrooms was utilized. All three classrooms demonstrated increases in the level of classwide on-task behavior as measured through direct observation, but mixed results were found for work completion, measured by teacher direct behavior ratings. Teachers generally rated the intervention as effective and relatively easy to implement.