Genie I am so sorry to hear this, but please don't let them grind you down. People like that should never be allowed to win at the expense of our dcs.
Its so hard to keep on fighting. I think we all know that only too well. Give yourself a couple of days to regroup and recover then go back and give them a good kick up the proverbials. We will be here to hold your hands while you do it.
My first thought about what to do next is - have your local Specialist School Inclusion/Autism Inclusion Team been in to observe him at all? Do you know if the school has even bothered to contact them? Ours hadn't. 
I didn't even know ours existed until a lovely lady at the assessment centre ds is on the waiting list for told me to call them.
I found out later that they should have brought them in when problems were first identified and at the very latest after the Paed had given his initial diagnosis of ASD. I spoke to them directly and they said if the school wouldn't bring them in I should get my GP to refer instead.
Less than one week later the inclusion lady did an observation of ds and came up with a frankly eyepopping report of his problems in class, plus a big list of recommendations to be implemented prior to formal involvement of the ASD team. She could see what his teachers plainly could not, probably on account of her specialist knowledge and experience in relation to children with autism in the classroom environment.
I was so sad and at the same time furious that he had got to year 4 in school with not one of his teachers bothering to raise how much he was struggling. The inclusion report made heartbreaking reading. Like your ds, my ds1 has a good standard of achievement and that's basically all they were interested in.
Once we had the report from the Inclusion Team (which incidentally only took a week) things started to improve for ds at school. He had moved seats, been given a wobble cushion (although I had to buy him one myself that suited his needs better), been given his own area for keeping his equipment etc etc Best of all, more of the staff have now been informed of his problems and he is finally getting more patience and understanding.
I think all LAs have Specialist Inclusion Teams. I found all the details about ours on the Local Council's website, so that might be a good place to start. Even if they have been in, if they are anything like our inclusion team, they will be angry that his problems are being sidelined and ignored and should want to help.
It sounds like none of these people know much about autism and therefore can't see an additional need or problem when its right in front of them.
I have been there, without the dx though. With noone believing that ds1 had a problem and treating me like a troublesome neurotic mother. I now know that his problems were plain to see for anyone who cared enough to look. I honestly think they didn't bring in the AIT because it meant they would either need to stretch their allocated hours, or purchase extra hours to accommodate ds's needs. Once again, it all comes down to money.