I generally agree with mrz - I think that there should be no special preparation - the test day should be a surprise for all and it just is taken in everyone's stride in Term III of Y6. It should be a snap shot and panic should only occur if the majority are under-performing - it shouldn't be an issue if one or two didn't do as well as expected. (And surely shouldn't there also be one or two who do better than expected anyway - all things being equal?)
I offered suggestions to Redrubber because she quite clearly said doing well on the KS2 SATs was important for the next school (for reasons she couldn't explain) - and I think in that case (presuming that a small improvement results in significant benefits) that may require additional support.
What I find very interesting is that nobody trusts the KS2 SATs - the press always doubt them, the next school usually re-tests (and TheFallenMadonna post isn't atypical) and this whole new L6 KS2 SAt papers dimension means some parents are now pressing for their DCs to achieve these heady heights, which from what I understood would be exceptional achievement. Anecdotal stories around here suggest that in terms of going to our nearest local secondary schools if you are in the top set you will be stretched and have homework and targets, but the lower sets just 'go through the motions'. This is a reality parents fear and in many cases probably truly face.
As someone who does a lot extra with my children I just want to stress this is because DD1 (Y4) couldn't read an analogue clock and wouldn't be able to if I hand't spent the time teaching her. DD1 (Y2) could barely add/ subtract up to 2 digits and if I hadn't intervened she'd probably still be floundering as many of her peers so clearly are still. DD2 was struggling with sounding out multi-syllable words and skipping words when reading out loud. We just kept battling on at home, after school moved her down a group and gave her books she read before for the rest of the school year.
So although I take the point mrz in a school with good teachers (as you clearly are) and well planned/ thought out lessons that progress and reinforce learning, then yes there really is no reason for a parent to intervene. But that isn't everywhere. If OFSTED rates our school GOOD and I'm having to do all this - please understand this isn't moaning, pushy PITA Mums posting here - this is desperately concerned, worried and floundering parents trying to do what little they can to rectify the abomination their child's education (in either state or private sector) can be at times.