If I was you, I would be honest with school and almost pin it back on them:
He’s moved into KS2, he has a sudden hate of school, it’s out of character with what we have experienced before and we see better behaviour at home. It is so bad that I am concerned about school refusal.
Is there something here that’s causing that?
What I’d want to know from this is what triggers have they identified that are the starting point for his behaviour.
Given that he’s got behavioural problems and that he’s awaiting an assessment for ADHD, is he on an individual educational plan - are the school receiving additional funding for him for special educational needs?
if he is, this opens the door for you to apply for an EHCP, if nothing else my lived experience in my area (and it varies wildly) was this speeded up diagnosis.
What it should mean is that there is a specific plan for your child on how they will achieve the standards expected of him. It should be presented to you every three months, and reviewed. I would have a read around ‘Assess, Plan, Do, Review’ which is generally the framework for it.
What strategies do you have in place for dealing with his overwhelm? Are there quiet spaces? What work do you do on emotional health/regulation/naming feelings? Is there support in class? How can we mirror this at home? What resources do you recommend?
I think here you’ll get a global understanding of how committed they are to helping and what their understanding is. If it’s a case of ‘nothing, Little Jonny needs to pull his socks up’ then I’d gear up for a fight because again, my experience is you’ll be down there once a fortnight having the same chat.
Make it formal, show you are taking it seriously. Ask for written notes with next steps to be emailed to you. If the notes come through and they are vague with no actions for school, or they have no timescales, query it.
My son was very similar at a very similar age. ASD and ADHD, although then we didn’t have the diagnosis. Had an IEP, flashes of anger borne out of frustration and overwhelm. Full on refusing to go in. Tears at the gate. Wouldn’t walk in, that kind of thing.
Half the battle was that despite having support workers in class he went largely unsupported because ‘other children have higher needs’. In the end, after 18 months of asking I wrote my own EHCP and it was awarded. Referrals for diagnosis became much quicker.
My biggest regret is spending 18 months debating and negotiating with school. Read the law, read the framework from your LA, arm yourself. Keep copies of everything they give you, and take them with you to meetings. If you decide to apply for an EHCP, you’ll need as much evidence as you can that it’s repeated, over time, with no improvement.
I wish I’d moved him into another school earlier, so don’t take anything off the table. We are now pre-teen, in a mainstream high school but that prides itself on its inclusion work. The difference is enormous. No school refusal. No outbursts of poor behaviour. Huge leaps in learning. Visibly less anxiety. It can be done. But don’t wait. The longer you leave it the harder it becomes.