Gosh that sounds tough.
What does he do if you help him dress?
My 6 yr old will faff and faff and faff in the mornings (well, most times really!), but I suspect the difference is that i can grab him and stand him up whilst dressing him super quick without him getting upset or resisting... And I work on the not getting distracted bit at other times of the day when it's not so fraught. He once got so upset about it all that he was in tears crying 'I don't know HOW to not get distracted, I can't do it'. Made me realise that he's not doing it on purpose, and he literally doesn't have that skill yet. It would be like pushing and nagging and following him round telling him to do the 6 times table when he has no idea what multiplication even is.
But I'm thinking that's not what happens for your DS? That you can't grab kindly and tickle him in between pulling clothes on him. That it's harder to even know where to begin teaching your DS some of these skills, when there are so many barriers in the way before you can even get to the core skill itself.
Sorry if this is rather teaching to suck eggs, but I think you need help with this. Lots and lots of help, expertise, advice, and support for you, and your DS.
Crucially, it's a long haul, a long slog, to getting him surrounded by people who know and want to teach and care and nurture him so he can grow and be happy, and shine.
The school sounds SHITE! I'm sure you've already thought about this, and are probably mid banging head for the millionth time on the ignorance and bureaucrasy and lack of funding.

