Each child is supposed to have an equal education. Your child is not getting one right now. It sounds as if the school is not giving your child "equal and fair education."
Check out special need forums. The people who are a part of the forum know all the ins and outs and should be able to either help you or steer you in the right direction.
At the very least, he needs a tutor half a day to come to the home, if they cannot provide for him at school for that half day.