Resurrect the mother bear within.

That doesn't mean your claws always have to show, and, in fact, they should only be for last resort, but you are his mom, and he needs you to keep pushing and advocating - all the way through school. I used to get sick just thinking about having to speak up, but if you don't, no one will, so you learn to do it even when it feels awful - and it gets easier over time.
You did good already speaking up, so now it will just take polite persistence to find a solution that works for your kiddo.
Let them know the signal isn't working and that he needs to just be able to get up and go.