Yes, he has a very good coping mechanism I think and we never force him to stay somewhere he’s unwilling if a bit of gentle encouragement doesn’t work. At school it’s different isn’t it.
He does sensory circuits first thing 4 mornings a week. They have a morning break and then lunch at 12:15. Plus they get choosing time (though I don’t know how this is earned or when). He has 6 (I think) tickets to allow him to leave the class for a 10m break but the idea is he’s done some work initially. He has a basket with all of his ‘jobs’ and he can choose the order in which he does them plus he joins in class lessons when he’s willing.
I think the problem in the afternoons can be (not always) that he doesn’t want to stay in the classroom much and wants a constant break.
When he leaves the class they may go to the library or different reading areas, hall if empty, office or possibly outside. He has been known to join in other classes PE sessions... 
I want to email the SENco with some ideas for them to try. I think the key is for them to use ABC to identify the issue/s and be proactive rather than reactive. He will have a new TA in the afternoons going forward. She is young and (hopefully keen) so maybe that will help.
liv congratulations on getting both kids out. A real achievement 
dimples I agree on the spellings. A reasonable adjustment surely?