The study, which investigated the influence of teacher behavior on the social participation of 4-year-old preschool children, was conducted in three phases: pretraining, training, and post-training. In the first phase, four preschool teachers were observed for approximately 30 minutes, 3 days a week, for a 2 week period during free play sessions at a university laboratory school. Their behaviors were then encoded according to the behaviors defined by Fagot (1973). The children's behaviors were coded according to the social participation behaviors defined by Parten (1932). Teacher behaviors which occurred most frequently during children's cooperative play at the pretraining phase were chosen for the training phase. Training sessions (held for 1/2 hour, 3 days a week, for a 2 week period) included instructional handouts to guide videotape viewing and daily feedback for classroom performance of training behaviors. Results indicated that videotape training was effective in increasing teacher play and observing behaviors. Children's behaviors changed when teacher behaviors changed. Increased amounts of associative and cooperative play were observed, while parallel and unoccupied behaviors decreased. Cooperative play only increased during the training phase of the study. (Author/AS)