The effects of class-wide self-monitoring on the on-task behaviors of preschoolers with developmental disabilities were determined. Also examined were whether the on-task behaviors of preschoolers with developmental disabilities had approximated the level of typically developing peers at the end of intervention, and classroom teachers and typically developing peers were interviewed on their opinions of the intervention. Four preschool children with developmental disabilities were involved in the research. In order to evaluate class-wide self-monitoring, a multiple-baseline design over the participants was used and replicated with three activities in the study. Class-wide self-monitoring was found to be effective in increasing the on-task behaviors of preschoolers with developmental disabilities, and their average on-task behaviors nearly approximated the average of the on-task behaviors of typically developing peers. Interviews were conducted to determine whether social validity indicated that the typically developing children and teachers expressed positive opinions of class-wide self-monitoring.