OK, ReallyTired, I think we have quite a bit of common ground. I'll excuse your implication that a good caning would deal with much of the bad behaviour, as I don't think you've thought it through. Would you use it on an abused child, an autistic child, a child with Down's, a deaf child, any of whom could be lashing out in frustration? I suspect you've too much humanity for that and wouldn't, not really.
In return, you'll have to excuse my parental bias in favour of my son getting the best academic AND social education he can (and he hates being bunged in a room full of other disruptive children, as it makes him hugely stressed and, importantly, inclined to copy their worst excesses).
Teachers at his very inclusive, very successful school tell me that he is an asset to the class. They also tell me that, yes, he still hums, whistles, exclaims, clicks pen lids, and leaves the room without warning. And none of his well-behaved, top-set classmates bat an eyelid. All credit to them for it; he'd have irritated the hell out of me at the same prissy age. I suppose you could regard it as 'irritant-proofing' them against annoying colleagues in later life?
In the early years of secondary he did spend some time each week in small groups, possibly a bit like your idea of nurture groups, but targeted at specific skills such as conversation, music therapy and OT. Mainly, though what he needs (and miraculously has) is a full-time, 1-to-1 TA, who negotiates his instant departure from the room when stressed AND then helps him to catch up on what he's missed that same day (and this is crucial; he needs to keep up on normal lessons, and you can't do this while being 'nurtured' in a cupboard somewhere).
He is, I'm fully aware, a huge cost to the state at the moment, but with hope of being a self-supporting adult at the end of it.
The problems, I'd say, come when you have a critical mass of bored, ready-for-mayhem types in a class, who see any disruption as a get-out-of-maths-free card...