Handicapped children, including the mentally disabled, were included in the public school system to the greatest degree possible. They may have had their own section of the school for the most part, but when they were physically or emotionally capable of participating in more mainstream classes - mainly in the art classes and gym - they were integrated into student body and school system taught all students from early on that everyone had abilities to contribute and not to be afraid of differences in the abilities of fellow students - and not to bully.
Though the "not to bully" never really took, the "don't be afraid of differences" tended to.
Though I didn't make many friends in school, I had several deaf acquaintances, one friend in a wheelchair with frightfully debilitating arthritis and probably Parkinson's (she died young - around 25), one with severe epilepsy, and there were several other adolescents with Downs syndrome that took several of the same elective classes I took in Jr. High School and High School.
Haele