People with mental disabilities often require more help and attention from teachers. They should have special teachers for those students. When they are put in classes with students with no mental disabilities, its your education that suffers.
We are taught to be fair to people not treat them equally. What is fair to one student may not be fair to another. for example while it is fair to let a mature 16 year old drive a nice car and go out to the movies alone it would not be fair to let a 16 year old drive a nice car and go out to the movies alone if mentally they think they are 5. It would also not be fair to give the 16 year old person 100 questions for a test and the 16 year old who thinks he is 5, 100 questions. quite simply because they think slower and it would not take that many questions for me to know if they understood the concept or not. does this help?