Although support in schools is supposed to be needs based, having a diagnosis can provide the additional push needed to get those needs met, as frankly getting the correct support is bloody hard at the best of times. If there is only one more space in the social skills group at school and your child has a diagnosis but another with similar needs doesn’t, your child’s diagnosis might get them in it.
Rightly or wrongly (ie wrongly) if challenging behaviours arise they tend to be viewed through the lens of the child having unmet needs if they have a diagnosis rather than just them being naughty, especially by those who have minimal knowledge of SEN or ASD.
If you have a name for it it can help the child understand and accept themselves.
As a parent I felt more able to advocate for my child with a diagnosis as I couldn’t be dismissed as easily as an overprotective/neurotic/whatever else parent and I didn’t doubt myself. Prior to the diagnosis I always had a niggling feeling that I was a crap parent even though I was pretty sure DC was autistic.
It allowed me, as a parent, to do what was best for my child rather than what was the accepted norm.
In the same way that adopters are encouraged to tell adopted children their story early so that there isn’t a big reveal, I think it is useful for children to know as early as they can that their brain is wired in a certain way which means that they like/are good at certain things and don’t like/struggle with certain other things. I think this helps protect their self esteem but it also removes the need to have to reveal their diagnosis to them. Unfortunately diagnosis is quite a medical procedure focusing on deficits. Being able to go through this when they are too young to really have much of a clue about what is going on is also useful. You can fall apart at the news and they won’t connect it with what’s being going on as well.
Having said all that, I don’t know whether shelling out for a private diagnosis is worth it. We got an NHS one before DS started school. There are sometimes problems with private diagnoses being accepted by LAs. You may be best saving your cash and spending it on private EP, OT and SALT reports should you need them for an EHCP appeal in the future. I really don’t know. It is a travesty that children are having to wait four years to be assessed. It shouldn’t matter whether they have a diagnosis, but it does.