An examination of the effects of enhanced milieu teaching procedures applied by parents on the sociolinguistic skills of their mentally retarded children is proposed. The purpose of the study is to determine the extent to which parent application of these hybrid teaching procedures can enhance the immediate and longer term development of linguistic skills, social communicative behavior and active language analysis strategies by their mentally retarded children. Parents in 72 dyads will be trained to use one of three intervention approaches: (a) Enhanced Milieu Teaching; (b) Regular Milieu Teaching; or (c) Responsive Interaction. The use of three comparison treatment groups and a nontreatment control group will allow us to isolate the contributions of the languagedirected and social behavior-direct portions of the Enhanced Milieu intervention, to compare the outcomes of Enhanced Milieu Teaching with those associated with the component models (Regular Milieu Teaching and Responsive Interaction) from which it was derived and to assess the impact of each treatment on children's sociolinguistic development. Measures of parent-child interaction, child acquisition of linguistic forms, child social communication within and outside the parent-child dyad, and child strategies for learning new language are proposed in a combined single subject and group design. Exploratory analyses of the impact of the interventions on children's social referencing are proposed. The results of this study will contribute to understanding how mentally retarded children learn all aspects of the language system and the potential impact of different types of parent input on child strategies for learning and language use.