We have a while before we need to make any decisions as ds is still only in year 4. I just don't know how you make the decision as to whether grammar school is right for your child. 
Ds is very talented at Maths and above average in other areas (not massively so). He is very competitive and always wants to be tested so he can improve his score. Likes doing crosswords and maths puzzles etc but hates writing and would rather watch paint dry than sit down and write a report or a diary.
We live in Bucks, Bucks only test on verbal reasoning. Ds would most probably do well in the 11+ as he has an aptitude towards that type of test. I bought one of those Bond verbal reasoning test books and ds completed the test without losing any marks. Being good at tests doesn't automatically mean that he is suited to a grammar school environment though does it? Ds isn't always that motivated to complete his homework and often needs a little push. Does that mean that he would find the pressure of grammar school too much or would it be good for him because it would stop him from coasting?
Lots of friends are already sending their children to tutors but I am reluctant to go down that route, I don't want him to pass the test because he has been coached and then find he struggles with the pace at grammar school. I like him to play in the park when he gets home from school I don't want him to be stuck with his head in a book all the time. He has an August birthday.