sorry honeybrown, been off-line. Would agree with what's been said already, though.
We didn't do the sunderland test, only because at the time there was a long wait and we were in one of those 'have to do something NOW' phases; also by that time ds2 was pretty much only eating food containing gluten or casein, which I think can be an indication.
We did casein first, and saw a big effect on his listening and 'speech', such as it was, within days, did gluten a few weeks later and within a week or so saw another shift; he kind of 'arrived'.
We have thought about doing the test since, but it would mean giving him those foods again to do the test, and tbh we're sure enough that it's made a diff to keep on it.
But I do know other children who've had no noticeable benefits from it, and it is a bit inconvenient and expensive, so would really agree that it's sensible to test first.
Interestingly ds2 now asks if something will 'make his head feel funny' if it's unfamiliar, doesn't want to try it if we say yes. He does remember how he used to be and talks about it, and knows that he doesn't have gluten, dairy or 'flavours'. It is hard to be sure what's having an effect, but he does seem to feel the connection himself.
Ours was a bit of an anecdote-driven, hit and miss approach; wish we'd had the benefit then of all these wise and experienced mumsnetters.