My DS does not go to an ABA school - mainly because living north of Watford there aren't any at primary level. He does have an ABA programme at home and at the ABA provider's office and 1/3 of his time is spent in a mainstream school with ABA support.
Many parents all over the country would love to send their children to ABA schools but there are hardly any - and those that do exist are almost all set up by parents. So its almost impossible to get them up and running as parents are reliant initially on fundraising etc. and you need a big enough group of dedicated parents to make this happen
A State funded free secondary school opened in Leeds last year set up by parents who all had children on ABA programmes. This is envisaged as a school across the spectrum including HF children accessing mainstream. However the cohort is dependent on which children the LA will fund. The parents were planning to fundraise to get the school open but in the end were able to jump on the free school wagon.
Treehouse in Muswell Hill started off similar way set up by parents in a library. It relied on fundraising until LAs started to send children there or enough children won places via Tribunal. It was aimed across the range - but due to funding decisions the cohort has moved to the more severe end.
Generally ABA (for children who need 1:1) is more expensive than LA special schools (higher staff ratio, higher qualified staff, more ongoing training and supervision) and so it is easier to get funding for children who are more severe and will be expensive wherever they are placed. Treehouse has much success at managing children who would otherwise be in more expensive residential placements.
So to an extent schools are defined by LA decisions and many LAs will not support indep schools and will want to place children in their own provision. Many LAs have a blanket ban on indep placements and every single parent has to go to tribunal to get one. My LA has a blanket ban on funding ABA even though none of the staff know anything about it. You have to go to tribunal and they fight you bitterly to the end to prevent it.
The LA EP actually recommended ABA having seen how well my son was doing with it, as did SLT. Both were made to change their evidence by SEN officers. At Tribunal we won a package of support ten times the provision the LA intended to pay. So the reasons against ABA are entirely financial. As Star says it will cost their adult social care budget dear in years to come. But LA staff are not very good at seeing beyond their own budget.
Having spoken to parents at both Lighthouse and Treehouse I think the schools develop their own curriculum over time. They are subject to OFSTED etc so are very highly scrutinised. ABA providers also will develop their own particular 'brand' of ABA. There are good and not so good private providers.
While I would not credit OFSTED with knowing much about SN their reports of Treehouse, Treetops etc give good - excellent ratings. There was a State primary school in Wales (Westwood) which had an ABA unit which also got great OFSTED rating but the LA shut it down a year or so ago for financial reasons.
Some good books to read are Sense and Nonsense. This is by USA provider with offices worldwide including Uk and explains the evidence base for ABA and the alternatives. In USA they work with many school districts and worldwide support children in mainstream. AP is involved in Lighthouse School (the parents who set it up all had children on AP programmes). Also by AP Its time for school which talks about setting up ABA classrooms or using ABA in mainstream schools.
You will also find ABA is used extensively in adult services. its somewhat ironic that having denied children access to ABA when they were young, when all else has failed many adult social care providers use behavioural methods.
I've read a lot of tribunal reports via voluntary work and its uncanny how when a child has been repeatedly failed and heading for residential suddenly the experts all start recommending ABA.
Keith Duffy (of boyzone fame) helped set up several ABA schools in Southern Ireland but again they have struggled to get LA financial support.
In terms of a career you should probably realise most of these schools are pretty precarious financially. But you would find the level of training and expertise and support to you as a teacher much higher quality than LA special school.