Mental retardation is characterized by “significantly subaverage intellectual functioning, existing concurrently with related limitations in two or more of the following adaptive skills areas: communication, self-care, home-living, social skills, community use, self-direction, health and safety, functional academics, leisure and work” (Luckerson et al., 1992, p. 5). Mental retardation thus applies to a broad range of children and adults, from those with mild deficits who function fairly well in society to those with extremely severe deficits who require a range of support in order to function. Regardless of the extent of mental retardation, the likelihood that communication development will be delayed is high. In fact, language delays or disorders are often an early outward signal of mental retardation.

Prior to the 1960s, a child who was diagnosed with mental retardation received little or no attention from investigators or practitioners in communication disorders because it was thought that the child could not learn and thus would make few gains in speech development. Following changes in policy and federal legislation, the 1960s saw the emergence of the modern scientific study of mental retardation. Since then, significant research findings about language and communication development have enhanced the speech, language, and communication outcomes for children and adults with mental retardation.

With respect to communication, children and adults with mental retardation can be broadly divided according to whether or not the individual speaks. Most children and adults with mental retardation or developmental disabilities do learn to communicate through speech, either spontaneously or with the aid of speech and language intervention during the developmental period (Rosenberg and Abbeduto, 1993). A substantial body of research has addressed the language and communication abilities of children and adults with mental retardation who speak. In particular, strong empirical findings about the communication abilities of children and adults with Down syndrome, fragile X syndrome, and Williams syndrome suggest a complex picture, with different relations between language comprehension and production and between language and cognition. The development of communicative and language intervention approaches for children with mental retardation who speak is an area of remarkable developments (Kaiser, 1993). Psycholinguistic research findings and behavioral instructional procedures have provided the foundation for language intervention protocols for teaching children with mental retardation specific speech and language skills. An early emphasis on direct instruction was followed by a shift away from the formal aspects of language and toward the teaching of lexical and pragmatic skills, measuring generalization, and the use of intervention approaches in a natural environment to promote the child's social competence. Techniques include milieu teaching, parent-implemented intervention, and peer-mediated approaches. These are each identifiable, distinct language interventions with supporting empirical evidence that they work. Perhaps the most important recent development is the extension of intervention approaches to infants and toddlers with developmental disabilities, a move reflecting examinations of interventions targeted to intentional communication and language comprehension (Bricker, 1993). Overall, the field has developed by expanding the content and focus of intervention programs and fine-tuning the procedures used to deliver the interventions. Greater sophistication in language intervention strategies now permits an examination of the relationship between the characteristics a child brings to the intervention and the attributes of the intervention itself.

Some children and adults with mental retardation, however, encounter significant difficulty developing oral communication skills. Such difficulty during childhood results in inability to express oneself, to maintain social contact with family, to develop friendships, and to function successfully in school. As the child moves through adolescence and into adulthood, inability to communicate continues to compromise his or her ability to participate in society, from accessing education and employment to engaging in leisure activities and personal relationships. For the most part, individuals who experience considerable difficulty communicating are those with the most significant degrees of mental retardation. They may also exhibit other disabilities, including seizure disorders, cerebral palsy, sensory impairments, or maladaptive behaviors. They range in age from very young children just beginning development to adults with a broad range of life experiences, including a history of institutionalization. These children and adults can and now do benefit from language and communication intervention focusing on the development and use of functional communication skills, although the areas of concentration vary with age and experience.

One intervention approach that has been developed for use with individuals with severe communication difficulties is augmentative and alternative communication (AAC). AAC encompasses all forms of communication, from simple gestures, manual signs and picture communication boards to American Sign Language and sophisticated computer-based devices that can speak in phrases and sentences for their users. Children with mental retardation who can benefit from AAC are usually identified based on communication profiles. The majority of children with mental retardation who use AAC have more severe forms of mental retardation. These children never develop any speech, or develop only a few words, or are echolalic. For them, AAC provides a means with which to develop receptive and expressive language skills (Romski and Sevcik, 1996).

See also communication skills of people with down syndrome; mental retardation and speech in children.