You can lodge an appeal to tribunal against Part 4, asking for the ABA school to be named, if that's the one you want. The LEA are just trying their luck, probably, hoping that you won't appeal.
You will need evidence to have a chance of winning this, as LEAs are notoriously anti-ABA (though SW London by reputation is more sympathetic). Evidence would be:
- School the LA are naming cannot meet his needs (it sounds like you have this evidence already which is great, you just need to get the prep school to write this in a report)
- Evidence that ABA is most efficient, effective and appropriate education for him - presumably you're doing ABA for him? You need reports from your consultant/provider etc (though bear in mind that if they do reports from VB MAPP this might not be recognised by tribunal).
- Report from Ed Psych backing up this view (if you want name of pro-ABA EP let me know).
The fact that the LEA are offering to pay school fees is positive, as it means they can't really argue against ABA school on cost alone as the fees will probably be comparable. So they'd have to argue that ABA is inappropriate/ineffective form of education - which is very hard for them to do especially if ds has made proven progress through ABA so far.
Surely its wrong to expect a prep school to take on a child who a specialist ADS unit will not take on?
Yes of course that is the case, and they have made themselves look like fools for suggesting it!
They might just be objecting over the fact the ABA school is out of borough - but if you can overcome any difficulties there (eg offer to pay for transport) they should easily back down.
An alternative would be having ABA support in a mainstream state school - again, the costs would be comparable to ss/ABA school.
Try this advocacy organisation, they took on our case for much less than a lawyer, and won.
Also worth registering on ABA Yahoo group and asking there. This is the main battle that ABA-parents go through so there is seasoned advice on the yahoo board as well as this one!