Rates of verbalizing by three children exhibiting moderate to severe language delays (delays of six months to two years) were increased through the systematic use of mands for verbalization, models for verbalization, and contingent positive consequences following utterances. Daily samples of each child's speech were collected during free play periods in a classroom for language deficient preschool children. In a multiple-baseline design across children, teachers prompted language usage and provided materials and services following request and descriptions. The results of the study showed that children's rates of verbalizations doubled to tripled from their baseline levels when the intervention was introduced. Subjects showed increases in vocabulary and complexity of utterances, as indicated by cumulative rates of novel words and novel word combinations. Generalization of newly trained words and grammatical structures to the classroom was also increased. (Author)