From my experience, I think that middle class/educated parents probably have more resources and skills to be able to find out what support is available and to fight for it, and that extends to all areas of support for children with SN (particularly for kids with HFA/AS/PDA, in my opinion).
I'm thinking about Shortbreaks and personal budgets in my area as an example - so not education, but a good example. Parents with children with severe learning difficulties or very complex special and medical needs (often children with a social worker) seem to be offered a fairly decent package of respite/shortbreaks/funding by the LA. But outside of that group, the parents who get the provision and funding are the ones who a) know about it and b) can confidently argue their case for it.
I had to do quite a bit of investigation even to find out about what was potentially available for my son, and then write a lengthy (honestly...prohibitively lengthy and complex!) form to access that support, even though my child is entitled to it. I was also able to question what his school and various therapists had written written in their supporting statements and get them to change things to better reflect his needs - to basically argue my point with professionals who are 'experts'.
So basically, unless you have a social worker to do all that for you, or can spend hours tracking down information and then confidently fill out a very long and complicated form (and understand the way it is 'scored')...you have little chance of ever getting that support.
This was just for one aspect of DS's support. Yet parents have to be able to employ this kind of energy and knowledge and confidence in their viewpoint over and over again - to get the right school pace, the right support in school, the correct benefits, respite, inclusive play opportunities etc etc. Its a BIG ask for, say, a single parent working and raising other children, or someone who has a basic level of education, or someone for whom English isn't their first language.
Is there a bias toward affluence in diagnosis? Does anyone know?
I would imagine so, although no hard evidence. I look at my DS sometimes - huge for his age, behaviourally challenging, mixed race - and think how many big, aggressive black boys are being a belled as 'difficult' and 'unruly' right now in London schools...but who don't have what DS has - two parents who are able, for a multitude of reasons but all related to our education and economic situation, to fight tooth and nail to have him understood and supported and not written off?
It makes my blood boil.