I have been reading posts on this subject for some time and would like to add my own thoughts to the debate if I might:
I have 2 nieces that attend North London Collegiate School. They both attended "evening classes" to supplement the learning they received at a nearby state school. One has always been exceptionally bright but her parents felt she needed additional stimulation to reach her potential. She entered NLCS at 11 on an academic scholarship and is proving to be an exceptional student there academically as she was in her state school. Her sister was regarded as bright and entered in the sixth form. She struggled for a couple of months as the level subjects are taught at surprised her but she knuckled down and is now in the top half of the cohort for each of her subjects. The most important points are that they are happy and doing well so everyone is happy so all is well for them.
I have a friend with kids at both Habs girls and boys. Both attended a an exceptional 'feeder' local prep school and the parents spent quality time teaching their children in all manners of ways. Conversation, holidays, reading, socialising. Both are enjoying school and placed midway within their cohorts. Again all is working out for them so their decisions were best for them.
My 4 year old daughter attended a state nursery after we removed her from a bog standard prep school in Milton Keynes for about 8 months and started to regress. She learned little or nothing in the state nursery but she was happy. We spent quality time at home conversing, practising writing, etc. We are fortunately blessed with a daughter that loves learning and questions everything and asks to practise her writing on many occasions. Anyway, we wanted her to be in an academic school that would challenge her adequately so that she would not be frustrated. We entered her into assessment at Guildford High Junior School without focussing on prepping anything we thought she would be tested on. That was our choice. We never even told her she was being assessed. Her happiness is the most important thing for us and that was what was best for her. She got in and is doing very well indeed and loving every moment in the school, which incidentally is exceptionally good. We are also happy about the choices we made on her behalf. Some have described it as a hot-house school. I have come to realise though, that it is described as such by by those whose children failed to get in there or those that failed to thrive there.
In my view, as parents we should want what is best for our children to be happy, thrive and reach their potential and should make judgements on what is best for them based on an honest personal view of who they are, their abilities, personality, what makes them happy and what they can be.
If you honestly think that they have huge potential and would thrive in a selectively academic and challenging environment, then help get them into one. No one gets prizes for trying and failing to get their child into a good school without the required support. It is a competitive world and there are many many children of high potential. If you want yours to do well relatively, spend time supporting them or find someone to do it for you if you cannot or do not want to do it yourself. Support can be provided in the form of parental time, a good prep school or tutoring. If we love our children and want what is best for them not us, we will be honest about them and do all we can to make sure they are happy and do well.
Please note that I am expressing my personal views to provide avenues for debate and not criticising anyone who has alternative views or looking for an argument.