Schools know naff all hun. Demand to see a specialist and wait and see what they say. Id also tell his school that you find the terms they have used offensive. He isent mentialy handicapt he just may have a learning disability and you want to see in writing what they are going to do to support your son.
Sometimes its not the child that has the problem but the teacher has a problem in teaching your child. Every child has a different way of learning and the teacher may not be able to adapt to your child. If your son's supposed problems were that bad they would have been picked up on way before now. Did he crawl, walk, talk ect on time? If he has compleated all his infant milestones on time then it may be the school are having problems teaching your child and not your child that has the problem.
Im saying this because when i was 6 my school turned around and said to my mam there was "thick" as my results were way behind, it took me mam ages to convince them to do a dyslexia test on my because i was "just thick". When she eventualy got it done, gess what im dyslexic and once i had that little bit of extra help my results were better than every one elses.