@ Rockpool - You know one day I must write a book on all this tutoring stuff because God knows, I've had some great ones, really awful and some interesting characters in between. Without any form of regulatory body, I swear it must be the biggest money making venture out there - just about anyone can claim to be a tutor. The bit I love most is when tutors for grammar schools and indies present their letters of glowing recommendation's from those they managed to get into their school's, which of course, don't include those that didn't. Bearing in mind also, they're not miracle workers and it takes a lot of support your end too. And just to make matters even more confusing, the most expensive are not always the best either. I've usually gone on recommendations, although a slight warning there also in that, one tutor I was recommenced was terrific in English (by the recommender's own admission), but weaker in Maths. Her kids were wearker in english, my ds was weaker in maths, but thicko me, not thinking that his Maths could be that bad, still used him. My ds's English got even better - wonderful in fact, maths improved not one bit. He was the most expensive.
For the age your dc, I once used a teacher at school (not his own, but from another year group) and she was fantastic. We had to leave the school eventually for other reasons and she was only able to tutor during school hours. I have spent eye watering amounts in Smiths on some good and some not so good books, still swear by Stephen Curran Books (especially if like me you're too daft to figure the tougher bits out yourself. My ds self taught himself Algebra using these) and also dabbled for a short while with Explore learning. If you're ultimately thinking grammars, start Bonds books as early as you can as I have known those who have avoided the cost of a tutor altogether, (or only required one just a for a couple of months before the exams).
You shouldn't really have to spend more than £15/hr at this stage and you may have to think about going to them. The reality is, all children respond differently to different types of learning. That said, one area I forgot to mention, which also keeps costs down if pennies are an issue, is group tutoring. Looking back, this was the MOST effective for my ds only because he's quite competitive and strived to be the best in his group. This, along with BBC Bitesize worked really well. I think, it's about figuring out your kids personality, lead learning style (i.e. visual, audio or kinaesthetic) and deciding from there:)