TooBloodyFedUp,
I hear you. I am in the same position. Eldest ds1 has been repeatedly and spectacularly let down by the school, but his two younger siblings are there and are both happy and doing well - not to mention the school is a two minute walk from my front door and I have an illness that often limits my mobility.
I spent years keeping them sweet, but in the end had to go in all guns blazing, not to mention getting him a statement myself. These days we have a 'cool' relationship. They don't like me, I don't like (some of) them, but we are civil and polite. My youngest will be starting Reception there next September, so I have 7 more years of having to rub along with them.
The SENCO and HT visibly twitch when they see me and the HT has been known to leg it in the other direction
but I get on fine with most of the teachers (barring a couple who were dreadful to/with ds1) and the infant teachers in particular are all lovely, having known me before ds's dx and knowing that I am not generally an unreasonable or unpleasant person.
Ds1 is leaving in July to go to Secondary and I can't wait to never have to have another meeting with the SENCO and be able to just blend into the background and be like all the other parents instead of constantly battling whilst desperately trying to keep the peace.
I agree with others that have said, get something in writing to them, so that you have it as evidence of them not being able to meet needs. You can word it very carefully, but a paper trail like this is invaluable if you want to get your dc placed elsewhere.