QS - I read your post in chat and came to find you.
I don't know about the system in Norway but in London, if the experience of my friends is anything to go by, you would have been referred on for family therapy, just so that you, as a family, would have been provided an arena for talking through how he is behaving, how he feels, how you all feel, and how, as a family, you can deal with it all. My friends have found it useful, because it's more emotional, rather than what is offered by the school which, while useful in its own way, is less in-depth and emotions-based.
The school referred my friends for this. Do they have anything like this in Norway?
Also, one of my friends has a dc who was taught in a year above his own. In some ways, it's very good (he was very frustrated by the academic slowness of his own chronological year, which would, ultimately, have led to behavioural and emotional issues) but ... it leads to issues of its own. The dc he was taught with were emotionally a year ahead and it did give rise to confusion sometimes.
A really great school should be aware that your son has gone through some major upheavals and has a lot on his plate to assimilate. Being academically ahead is an issue, being in a year older than your own is an issue. From the experience of friends, I'd be hoping the school would be doing lots of talking; bringing you into school to talk to you, too.
I can only speak from the experience of friends, I'm not a teacher, but my dc's school would have very regular, though informal, talks with you.
Here's the hard part - how is your ds with understanding social behaviour? I skim read your thread and you all seem a v. emotionally literate family. It may well all come down to a slight chronological immaturity and a degree of frustration. Also, don't boys get testosterone spurts where things go a bit pear-shaped for a bit?
But ... there is something about v. bright kids and reading social behaviour. It doesn't always signify a SN, but it can do. And even if it's not something like that, it can be just something about academically being so advanced and the social/emotional stuff just being at a different level.
I've been there with mine. We did wonder at one point is he might be slightly on the autistic spectrum, but I think, atm, that it was more that some bits of him were very mature, and frustrated, while other bits were running at a different speed.
Anyway, long post, but I think a school in London would also be looking at that, possibly with a referral to an Ed Psych.
Hth.