I'd go ahead with the Math's (anything that's in KS2) there isn't a test I've heard of that doesn't have a large Math's component. For English I'd recommend concentrating on extending DC's vocabulary, that helps in VR if they go that way and also in comprehension and cloze if they go that way.
Everything else is still up for grabs so I'd wait until the announcement in a few months (if KCC ever get their act together) before starting anything more specific.
I always think a good grounding in Math's and English is never wasted whatever school your DC goes on to so it's worth doing whatever happens with the test anyway!
Many thanks. We have been doing some extra English anyway as the school has been using Schofield Englaish MA type books but thats great advice.