I think you need to be clear whether this is the full North Carolina Teacch approach, or whether it is eclectic provision which is using aspects of Teacch.
Teacch done properly is a whole environment approach and autism specific education - which is why they are probably say they are using it as you are asking for a different type of autism specific education ABA.
The environment is changed to make it easier for the child (and imo the teacher!) and then very clear prompts are used to guide / support the child. So in a pure Teacch environment (and if you have a NAS school near you you can go and visit and see it) it will mean white walls, no distracting environments, the child will have a workstation and usually required to complete 'work' presented in boxes. So its very clear the child has to do the task in box 1 - then box 2 etc. This is called teaching the child to work independently. There is very heavy use of visual symbols and schedules to tell the child what to do next. The child usually works on their own away from all distractions.
So it is very different than the child led eclectic approaches usually used in mainstream by LAs where they use bits of Teacch eg the use of visuals, schedules, sand timers etc; but don't go for the whole adult / environment directed approach. Often the room is laid out with very clear visual markers as to what each area should be used for.
I am not a fan of the eclectic teacch - DS was exposed to as it was just these generic strategies eg symbols on a keyring, visual timetable, sand timer etc with no adjustment for eg the fact he could speak and follow verbal instructions. ABA uses prompts but fades them out asap. Teaach builds the prompts in and seems to leave them there forever.
My view and I know others on here have different experiences - is that it is useful for children who are lower functioning and would be unlikely to develop the ability to do tasks fully independently - I would still like them to try ABA first to check this out - but I can see it is useful for that cohort who do not succeed with ABA and perhaps have for other reasons eg SLD limited life prospects. But I really do not like it being used for children who have far greater potential and who can learn to access learning independently if taught the skills to do so. My worry about Teaach is what happens when you leave school and go into the real world, and the work is not organised for you, the environment isn't artificial and people don't carry round symbols on velcro. For children who will grow into adults with a high level of dependency then they will always have that support. But for higher functioning children I feel it is disabling them not to teach them how to cope in the real world.
Through ABA DS has learnt to follow verbal instructions, to follow cues from other children, to follow group rather than individual instructions etc etc, he copes brilliantly in a typical classroom environment. So I would prefer him to be taught to live in the world as it really is, not a world which is artificially and permanently changed for him and leaves him still unable to access the real world.
However I have to say I have never seen really good Teacch teaching. DS would never qualify for an NAS school. His IQ is too high and he does not have very challenging behaviour. So I don't actually know how a autism specific school would have used Teacch for a child with a high IQ.
I do know you should check out the CVs and qualifications of the staff who will be teaching Teacch. Teacch proper only accredits people to train others if they are properly qualified. The vast majority of LAs send their staff eg outreach on a 5 day TEACCH course (sometime called structured teaching course), and probably 1 or 2 on an advanced course. But there is no follow up. You do the 5 days course and then call yourself an expert in Teacch and train others to do it. I cannot think of any other discipline where you would sit in college for 5 days and come out supposedly equipped to implement what you have learnt with no supervision or monitoring, no updating, no evaluation and also sufficiently experienced in the approach to become a trainer yourself. eg I have done a course on brain surgery therefore I am equipped to do brain surgery and teach others how to do it. Its ludicrous.
I would ask for the Cvs of your ABA staff and the LA staff eg outreach teachers who will be doing the training. I would look at the Dept of Ed stats for their outcomes eg the SEN attainment gap and see how they fare eg % of children who achieve at SATS levels. You could ask the LA if they keep specific data on the outcomes of children who have had Teacch.
DH emailed North Carolina and asked for details of how someone would become accredited to train others in Teacch and surprise surprise none of the LA staff were so accredited (the same is usually true for PECs they do the basic course but don't get accredited to teach others how to use PECS).
Reserach Autism gives Teacch less credibility in research terms than ABA.
The US National Standards Project - email me if its disappeared offline - says Teacch did not have enough evidence to be considered an established treatment and recommended only established treatments were used and only if this failed would other approaches eg Teacch be used.
When it came out it was a big step forward in helping children to learn who previously were considered incapable of being educated - but I think we have now found better ways. ABA does not work for every child, but it gets considerably higher success rate.
Most LAs are obsessed with Teacch - I suspect because its cheap - a 5 day course rather than for ABA supervisor level 5 years, of ABA consultant 10 years.
That said there are special ed teachers out there who are naturals and use teacch and like it and learn on the job and develop their own system for the individual child and do get good results. But they are few, and usually only found in special schools. In mainstream it is not teacch your child will be getting, but a very very watered down version and usually not individualised to the child.
And yes I would suspect visuals would very definitely be used even for a verbal child. They were with mine.
The other problem with Teacch is that organisations like NAS use it in their schools and depsite saying they do not advocate one particular approach, clearly do as they recommend SPELL (you guessed it based on Teacch).
However if you went to North Carolina you may well see something approaching good practice. But I doubt you will find much of it in the UK.
You need to quote SCAMP study for ABA. Look on research autism.
An argument for ABA rather than Teacch is that some children progress through ABA to a point where they can learn in a typical classroom alongside their peers with or without support. As I understand it children who do Teacch tend to always need support - LAs expect those children to have support throughout school. So there is an argument of perhaps 3-4 years intensive ABA -v- a school lifetime of less expensive support. The downside to this is you do not know if your particular child will be one of the ones who will graduate from services.
Another argument is that you know ABA works well, whereas Teacch is untested. This is difficult as tribunals will often send you off to try cheaper options first. DS had what I call Teacch-lite for 18 months and learnt nothing this way at all. The LA said it was because we did not engage with it - this was not true - although we did object to the really bonkers stuff like not using speech, when he could talk. But I would say this was teacch done really really badly - but I think in UK in mainstream it usually is done really really badly.