I would just like to put forward a very personal view, my own experience - no statistics etc.
Just a year ago, I would have disagreed with a lot of what Northcoteluvvie has been saying, from a state school background (husband also). But I have found her information re. the prep school system very insightful - thank you, particulary with events this recent year. My kids (3 of them) have all attended one of the most popular state primarys in the area and I always wondered, if you are lucky enough to get into one of these 'best' pimary schools, why on earth you would chose private over state and spent so much money and would have dimissed the advantages. These schools, have traditionally always managed to get most, if not all, kids who were always going to go private, into the top private schools ( yes, with an hour tutoring each week ) - usually around 50%, which has been the case, as far as I know, for the last 6 years, I have an older child of 18, who got into Allyens, Wimbldon and Clapham and Streatham - but, after much deliberation, we decided we just couldn't afford it, at that time.
But just this year, there has been a massive shift, having recently had a Daughter start at Emmanuel in Sept. She is a bright kid - not a genius, but as bright as her sister - if not brighter. We though she would have had no trouble getting into Allyens etc. and despite getting a super high result in the Wandsworth test and doing really well in entrance exams, the offers she got were from Emmanuel and Steatham and Clapham. Basically, the competion is fierce out there now and I know of parents who could have easily afforded/and wanted to send their children to private schools - who didn't get into ANY private schools and have sent their children to state school. I find more and more 'normal' (not so affluent parents) taking their kids out of these state schools earlier, to avoid the hassle at 11+, to get their kids into the private system ( a lot of what Nothcoteluvvie is saying, is unfortunately true )- if that's what you want.
It is now absolutely wrong to presume, Emmanuel and Clapham and Streatham are 'fall back' schools, their intake is demanding a higher and higher pass rate - too high for most. I find this trend really worrying, I always liked the idea, of a less academic, all-rounded school, we are a Arty family and Emmanuel, in particular, has valued other properties - as important as the academic and I fear this is changing fast and such a school, in future will not exsist. I am just observing, with the experience of having an older child. We sent our eldest to a good state Church school, she has done well, but had personal problems, which I won't go into, but it has been difficult- nothing to do with the school - which is why we sent our second private, to try to make it as easy/simple as pos - no guantees, I know....
My post isn't to scare monger, but to hopefully put forward a different perspective.... is your child a true academic/genius ? - looking to the city/ Eton/oxbridge - at this point in time, I would advise getting them into the private sector as soon as pos. to get them into one of the top private schools - the competiton is crazy. Do you want all all-rounded balanced education, between academic and the Arts/ Music/sports and social ?- then get them into the best state or private school you possibily can - they will do well, but I do fear all these schools are going down the same academic route, blame it on worldwide pressure on competing with China etc.- who knows...So much pressure is placed on teenagers at the moment and with the benefit of hindsight, I would not have focused so much on the academic with my eldest, even though she was very bright, the most important thing for them,is to be happy and well rounded. Don't place too much importance on the academic, a bright child will find their way. I know friends with children of the same abilitly as my eldest who got their kids into City Girls etc. ( 6 years ago - unlikely they would get in now) they are suffering from being the less able in the class- leading to low self esteem, amongst other, more serious problems. Be as realistic for your child as possible,in my experience, it is better for them to feel 'on top' at a less academic school. I suppose my point is; the academic bar, is being raised all the time, to almost unrealistic levels and lots of teenagers just aren't coping, where will this all end? Just make sure your child is happy and well rounded, then you will have absolutely have done your best for them. Please do not pick me up for any grammer errors, I am state school educated- remember!