God that's hard. I used to teach an ASD student who was very sensitive to perceived criticism to the extent that I had to be very careful with addressing the class as a whole Will you all quieten down a bit? as he took the you personally and would think I was targetting him. He would have HATED this.
Another student I had had the removal room card so if HE felt he was going to blow at any time he would flash it and walk. This was monitored obviously by the removal room staff so it could be followed up whether it was an instruction/ a particular class/subject/time/member of staff but it wasn't for a whole day, that is Exclusion/solitary is for a behavioural incident like fighting for goodness sake.
The non-participation or doing something else entirely scenarios ARE hard to deal with....I had a boy who would do beautiful drawings rather than his classwork so he was told it would be a comment to mum in his logbook if he didn't complete the core or he would have to do it in his own time or for extra homework. This usually did the trick as did turning a blind eye if he was drawing whilst I teacher-talked as he was often taking it all in at the same time iyswim. I would occasionally allow him 5 min doodle between tasks to keep him on task.
Another boy hated repeating things he knew and deemed it a waste of time so was told the same as any student saying the same: you are repeating it for practise/if you have done it once before you will do it perfectly this time/ a chance for you to show off what you know. Didn't always work but didn't lead to meltdowns either.
Another boy was being forced to learn a language
when one-to-one/key skills/social skills- situation/non verbal cues recognition/ extra English would have been far more appropriate.
I was told his target was simply to stay in class and try to take part....he sat there bless him and was zoned out/bored/bemused 90% of the time but he did have a quirky sense of humour and if I tapped into that then I could cajole him into bits and pieces (he was able to drop the subject at end of year 9 but should have been allowed to opt out earlier imho).
My point? All members of staff should be given strategy training along with a list of triggers/behaviours observed by the TA. The student should not have the onus of recognising or expressing when he/she is about to lose it as sometimes that is asking the impossible. The teacher should also be able to recognise some of the signs or triggers especially if there is spill over from previous lesson.
The removal room ought to be used positively with a card for student to take time out if needed as a sanctuary rather than a punishment.
None of that is rocket science. Yes your son needs to be treated like others and accept consequences to (in)actions/ boundaries in place BUT there has to be some flexibility in dealing with perceived inflexibility surely? Unless he is a danger to himself and/or others I would hate to see him removed like this as it isn't tackling the issue at hand which is how to engage him/ how to encourage him. I don't know - having a packet of disinfectant wet wipes for him to wipe his desk pre equipment could be part of his particular routine.
Many of my students were supported by their classmates btw They would let me know if something had kicked off previously and they were adaptable in understanding the outcomes/expectations for some of their peers might be different NOT lower, just different in approach. Differentiation is always hard...the all/most/some method tends to dominate but is often lip-service compared with how spot-on some primaries get it with differentiated tables and tasks. But all his teachers ought to be striving for differentiated activities rather than teaching to the middle.