Hi OP, I'm mum to ND teen, who was notably different from 5, but took until 10 to diagnose.
I always read posts like this to see if there are any similarities with DS to let the OP know, but in this case, really there aren't. DS has ADHD F90 moderate - severe.
What I would say, is go private for the diagnosis as soon as you can. Once you have that, you can take it to the NHS and use their consultants.
From 5, all his school would say, was, "have you considered autism?" No. I haven't, I'll look....no, that doesn't really fit how DS is, do you have any other thoughts. "Ummmm, we can get someone in to assess him for autism" No, I really don't think that's it. "So, shall we get someone in to assess him for autism?" FFS. Sure, if that's the only word you know. "Ok, so his assessment came back that it's not autism" fuck a duck, you don't say Fine, so what do they think it might be then? "Oh, they don't look for other conditions, it's just an autism assessment" Thanks for that. Meanwhile, we'd been on a waiting list to get an assessment via the NHS for nearly 2yrs and had only had one GP appointment as part of that process and remained in the queue for the next step.
When I finally had enough of no one doing anything and the senco team being more than useless, I went private.
Private consultant: Session one, just me, explaining DS and his behaviour. Session two, her with DS for literally 1.5hrs while I sat quiet on the sidelines. A phone call the next day to explain his almost textbook diagnosis of ADHD, the paper work will be in the post tomorrow, please take this to your GP and fast track to their ADHD consultants at the hospital.
Also this meant evidence to put with our DLA claim. I can now claim carers allowance too. Financially this brings in over £700 p/mth, which helps no end with replacing things he breaks and that it's very hard for me to get any work done because I'm permanently in meetings with doctors/schools/having to sort out the latest incident he's involved in.
As soon as you can, I'd recommend a private diagnosis. It's one hit of cost, but worth its weight in gold.