Sassh, that sounds like a great option for a family that already hate the school and most of the teachers.
Sometimes you have to do what's best for your child. A protracted legal complaint under dda would hardly improve the situation.
It might make it slightly easier for any child that follows, but tbh, such schools usually learn from their mistakes and make it impossible for sn children to attend the school in future, by some roundabout method that gets them away from the discrimination hoop.
It's very worthy to take on that sort of thing, but even if you win, you are left with a bunch of teachers that you already hate, and now a school that includes your child under duress.
Sometimes a 'win' is pretty much a lose, after all, especially if there are other options.
Op, why do you want him to attend the senior school when they exclude him routinely?