Yes, I wrote a longer post about him above. We are abroad so he has only just started his second year of school. Last year was a complete disaster until he started ADHD medication, then it was OK.
To be honest it is difficult to say what kind of school would be best. The thing is that DS2 has challenging behaviour as well, which we understand now was basically him getting overwhelmed, but we didn't really understand the full picture initially. This started probably around age 3-4. Before school, he went through three different Kindergartens which is most like nursery in the UK system, but goes until they are 6 or 7, so it does include an aspect of early years education which is mostly learning through play. Kindergarten was also tricky for him until we found this last one which was just brilliant because the director is fab and will move things around until the right mix is found. She shifted some stuff for us so that DS could join the one group with a male staff member because it just so happened that he'd had previously better experiences with male Kindergarten staff, and coincidentally it turned out to be a fantastic fit because this bloke was patient, kind, soft-spoken and coincidentally had a few overlapping interests with DH so when DS rabbited on about things his dad likes, the staff member recognised them and was able to engage on that level.
Part of what didn't work initially at school was that he does not come across well to new adults particularly when he is part of a group. It was often fine when he was little and not really expected to follow instructions, but maybe starting at 3-4 and certainly once he turned about 5, people would see his behaviour before they would see him and that's where the pattern became much clearer, because he does not generalise social rules or automatically recognise adult authority, and so he would either try to explore something inappropriately or just want to deviate from whatever the adult-led activity was supposed to be. So they would (understandably) try to immediately set a boundary and stop the behaviour, and if they did this gently he would ignore it, but if they escalated to even slightly stern, this would basically cause him to mentally categorise that adult as a scary person who cannot be trusted, and when he does not trust somebody then he would barely engage with them at all, which meant he was not following instructions or really listening. We did not initially recognise this because if a trusted adult tells him a rule, he will want to follow that rule to the letter and so we didn't really have issues with difficult behaviour at home (at least not then) because he trusted us and listened to us. In addition to this he has some stims (which come out when he is overwhelmed) such as loud vocalisation which can be annoying and disruptive, and he can also be prone to silly/attention-seeking/over-emotional type behaviour when overwhelmed as well, and he really can't seem to stop himself from doing this, or hold any kind of serious conversation about it afterwards either. (this all goes away with medication, and comes back literally as soon as it wears off).
The only adults who were able to actually get anything out of him were people who had the time and curiosity to meet him on his level, who were able to let him take the lead and follow him into his world, and then once that relationship was built, they could successfully lead him into other places.
Looking back at that, I can appreciate that actually this just isn't practical for schools. He did well on a 1:1 basis, and schools don't have the staff to gently and individually welcome every single child in this way, especially when there are 30 of them starting at a time. I think maybe I was naive because my eldest child being much older did receive a 1:1 (or, actually 2:1) home visit from his nursery/reception teacher before he started at nursery and I don't think schools generally do this any more. I do think if DS2 had been able to have just 15 minutes to meet with the teacher and see the classroom before he was thrown into the whole class situation with 25 other people in the room he would have done much better but it was not an option, unfortunately. And it might not have been enough - even his favourite ever Kindergarten teacher once he stepped back and was less involved directly, DS would have good days and bad days and still basically would not engage with any of the other teachers (but particularly the ones who thought he was just naughty). So I suppose if I was looking at schools, I'd ask whether there is any kind of scope for a slower or gentler introduction. With small class sizes, at least for us, the issue is that unless the class was like 6 pupils, it wouldn't have been small enough to make a difference. We were looking at this at one point and I don't think even SEN schools are that small here. Learning through play is always a positive IMO over academics for younger children, but the reason he wasn't totally drowning at Kindergarten was less because it was play based and more because he had more freedom/autonomy to choose his own activity most of the time. Schools incorporating autonomy can be amazing, but the good ones seem to be really really rare. Beware of schools which have this as a buzzword but do not actually have staff who are trained and experienced in supporting it adequately, as it can end up like Lord of the Flies. Large school with good SENCo might be good, but might also be a magnet for all the SEN pupils in the area which might mean you're fighting for scant resources or the school is overwhelmed by the needs and the teachers can't balance it all.
There's no easy answer. I would visit the schools, see if they will let him come for a visit, and see what your gut says. It's usually a good indicator. Don't stress about finding the perfect school, because chances are that a lot of it will be down to luck and you just can't control the outcome all that much and actually, you will drive yourself mad trying (seriously. This is a genuine risk and sometimes you have to step back and let the system fail.) Put your efforts into observing his patterns so you can basically be his "translator". That is the best advice a family member who is also a SEN mum (and was a SEN TA for a while) gave me.