My son (born June 1996) has just taken exams for KE Camphill/Aston, Queen Mary's Walsall and Bishop Veseys.
My experience tells me that you (the parents) must remain chilled and encourage your child to do their best - not put them under pressure to achieve. Neither would I engage a tutor. Firstly, it costs a fortune (I certainly couldn't afford it!), secondly, the KE exam in particular was very tough and most of my son's friends who had undergone months (and also years) of tutoring, found themselves in a panic because it was nothing like they had done before. My son, on the other hand, was very relaxed and felt he had done well - so many of the candidates entered the exam centre crying or white with fear - many more exited in tears and were scared to meet their parents. Indeed, some parents were nagging and testing their children right up until they went to their test room - how inappropriate!?
I did about 5 hours of test papers from WH Smiths with my son so that he was familiar with the format, nothing more. My firm belief is that you should only have a child at a selective school if they are able to prosper there, regardless. For example, my 13 year old nephew is at the Walsall Grammar School and he had the same 5 hours coaching from me - he was then on the waiting list for 2 days (i.e. not an automatic pass). Yet he has been at the school for 3 years now and is excelling at every subject (will be entered for 3 GCSE's a year early and is 'gifted and talented'!). On the other hand, many of his classmates (who would have got better entrance exam results than him) are struggling and having to undergo literacy and numeracy support!! Do you want your child to feel like a permanent under-achiever or feel happy and able at school? I will be happy with whichever school my son is allocated, even if it is the local Academy, where I am sure there is every chance he will do well if he enjoys it and is encouraged to do well by teachers and me and his dad.
Good luck anyway - it can be stressful, but don't let it be - feeling able to pursue an interest or passion can lead to a very successful life and I should know!