The social environment of elementary school is vastly different from that of kindergarten. First-grade children are likely to have diffıculty adapting to those differences, as seen in their academic performance and communication. They express this by, for example, leaving the classroom without permission during class and having conflicts with their classmates. A possible way to ease the transition to fırst grade is to implement consistent support of children before they enter elementary school. The present study evaluates effects of a class-participation program to support 2 preschool children with developmental disabilities. A comprehensive assessment found that both children had already acquired class participation behaviors. However, the frequency of occurrence of the appropriate behaviors was low, and inappropriate behavior and irrelevant remarks during class often occurred. Therefore, the intervention program focused on the following: (a) establishing an environmental setting that resembled the elementary school classroom, (b) clarifying the teachers' and supporters' roles, and (c) giving defınite and immediate reinforcement for all class participation behavior. During the intervention, the rate of occurrence of active participation in the class increased. After the intervention, the participants maintained correct behavior during class. Furthermore, the problem behaviors of speaking in a loud voice and standing up inappropriately in the classroom were not observed in the post-intervention period. On a measure of social validity, teachers and supporters reported that the children's attitude toward participating in the class had signifıcantly improved. These results suggest that the class-participation support program may have been effective in promoting appropriate behavior in class in 2 children with developmental disabilities.