Good luck CelticWorrier, I'm sure you will be fine. Hello again Desperado99, hope all is well with you!
Half the battle is that the child is motivated and it sounds like your Son wants it as much as you. I too when through bouts of buying up everything that had 11+ in the title and ended up selling it all myself at a quarter of the price as we just didn't use it all!
We are out of County (Newark) and it is hard when there is no support at primary, all the other Yr 5 parents have their own opinions of secondary schooling and those that also want grammar are so secretive about what preparation they are or aren't doing (in my own experience anyway!) it can be a nightmare. I can honestly say this site saved my sanity, and is the reason I'm back on it this year to hopefully give back some of the support I received this time last year!
Anyway, Kings has no catchment so being out of County really doesn't matter and if this years results are anything to go by, scores weren't as high as they have been in previous years.
If you have any queries, ask away and there will always be someone who can offer an answer or at least suggest a glass (or two) of wine and some chocolate - believe me, you'll need it come September!!!