The communicative interactions of mildly delayed and normally developing preschool children were recorded during free play as they interacted with children at different developmental levels in a mainstreamed program. Analyses of syntactic complexity, semantic diversity, functional aspects of speech, and the use of selected discourse devices indicated that mildly delayed children adjusted important characteristics of their speech in accordance with the cognitive and linguistic levels of their companions. Specifically, speech addressed to less developmentally advanced children was less complex, more diverse, and consisted of a greater proportion of behavior requests but contained proportionally fewer information requests or information statements. These adjustments appeared to be well suited for improving communicative effectiveness and were similar in magnitude and direction to those of normally developing children. In addition, both mildly delayed and normally developing groups were generally successful in obtaining responses to their behavior and information requests. The implications of these findings were discussed in relation to the communicative competence of young children and to early childhood mainstreaming.