The one thing I've realised about the KE exam is it pretty genuinely tests whether your child is actually bright or not. Yes tutoring is necessary in my opinion and if you have a good tutor it can bring out the best in your child (but partly tutoring is needed because everyone else is being tutored! )
General brightness means a strong vocab and great comprehension, being articulate, being confident and happy to take on a challenge, and of course having a strong maths ability, including in problem solving.
Clearly Bond is useful but just too narrow. If I had my time again (and luckily I do because my son is the eldest of 5) I would encourage more and wider reading, reading aloud, more discussion, talking, debate, and working from wider workbooks than just the 11 plus ones.
The AE Vocab series is also good to start in Yr 4 provided you're going to monitor and talk about the words as they come up. Likewise Schonnell's which was recommended by a tutor.
If your kid dosn't get in to Grammar the work will not have been wasted - you were have a hopefully strongly literate child who loves study for the sake of it, rather than just to pass exams etc.
I don't know if this will be pasted out by admin, but I've also found that magazines like Aquila and National Geographic Kids are great for keeping children 'alive' to learning. Hope you get what I mean - I'd rather have a kids that was mentally 'alive' and thirsty for knowledge than one that can just churn through Bond at 90% and hates it..