My aunt, Sara Beth, was born with a mental disability. At birth she had a lack of oxygen which, in turn, caused disruption in her brain. She knew enough to know that she was different from everyone else and that she would never be able to live a "normal" life. Sara Beth has had an unimaginably positive affect on me. She has made me less judgmental, more patient, and more receptive to everyone's special needs.
The authors of our psychology book use the term "mental retardation", or "intellectual disability" to describe people that have an IQ below 70, have inadequate adaptive functioning, and have theses symptoms prior to adulthood. One percent of Americans have mental disabilities based on the previously mentioned criteria. Societal attitudes towards people with mental disabilities has dramatically improved over the last 60 years. Families used to lock their children away if they had a disability. People didn't think these children could learn or function in society. They have since been proven wrong though.

"The Americans with Disabilities Act (ADA), passed in 1990, outlawed job and educational discrimination on the basis of mental and physical disabilites (Lilienfeld 335)." "The Individuals with Disabilites Education Act (IDEA), passed in 1996, provided federal aid to states and local educational districts for accommodations to youth with mental and physical disabilites (335)." In today's society, many kids with disabilites are mainstreamed into school and interact with kids who do and don't have disabilities.
I think it's important for everyone to understand that people with mental disabilities are capable. They have special talents, pet peeves, and bad days just like everyone else.