Speech-Language Pathology/Stuttering/Mentally Retarded Stuttering
Oliver Bloodstein wrote in his book A Handbook on Stuttering of "ample evidence" that stuttering is especially prevalent among persons with mental disabilities. Stuttering seems to be especially common among persons with Down Syndrome. There is some debate about this, as the stuttering symptoms among the developmentally-delayed can be different from stuttering in adults of normal intelligence.
Developmentally-delayed individuals tend to have other speech and language problems as well. A speech pathologist treating a mentally-retarded person will probably use more than just stuttering therapies. There are books devoted to this, such as Communication Strategies for People with Developmental Disabilities: Issues for Theory and Practice, edited by Ken Linfoot, Ph.D. (1995, Baltimore: Brookes Publishing Company, $33, 800/638-3775).
Eugene Cooper suggests that "reducing the number of abstract concepts the clinician uses" is paramount in treating mentally-retarded stutterers. He also emphasizes that therapy should focus on helping mentally-retarded stutterers "identify and express their feelings and attitudes about the problem." Too often, speech pathologists act as if mentally-retarded persons lack feelings and emotions, as well as intelligence. Cooper also writes that the stutterer should be "capable of verbalizing the goal of the procedure and their desire to achieve that goal" (Cooper, 1986)- good advice with any stutterer.
If the person likes to play video games, you may want to try some of the speech therapy computer games.