As an old and tired mum of 3 DS's, I can comment on my experience for some of the questions on this Thread. DS1 offered co-curricular scholarships at 13+ for DC (top Scholarship) W and (alsoTop at another School), tried to negotiate with W for more on the basis of the DC scholarship - no luck. DS2 got to interview stage at W(11+) but wait listed at number 10 on the wait list. Unfortunately, Wait list did not move at all that year. (Received both a fat envelope and a thin envelope on offer day!).
DS1 now in sixth form, yes W do cull as other schools do, but the points system is not too taxing, for example in theory you could have enough points (21 required) to stay on at W with 11 B's, practically it is more difficult in that you need A's at GCSE to continue with Maths/Sciences/Languages. There is a lot of extra help available to anyone who wants it, Clinc's etc, teacher's always offer to be sought out for questions etc. DS1, was bottom 3rd for a few subjects, in fact probably bottom 10% for language (still achieved an A* at iGCSE), He had a total of 40 points.
Yes you are required to have a C at AS to continue to the A2 course, but if you don't make it you can repeat the year to get your grades up, or change to subjects that might suit you better as one of DS friends did. DS2 very happy elsewhere and has developed no end, couldn't move him with a barge pole if we tried.
DS3 likely to do W 11+ next year along with 13+ pretests for St P's and KCS where his HM wants to go, but his own heart lies with W. So I will be on here next year which promises to be a very nail biting year for us with A2's, Uni Applications, GCSE's and 11+ all going on at the same time!. We have been delighted with W to date, I can't fault it. Even at it's current fees (we don't know increases for other schools at yet for 2014) it is on par with DC, KGS, Emanuel, cheaper than KCS, St P's, Epsom, StJohn's and Reeds. School fees are not for the faint hearted, though they do make me feel faint hearted most of the time. Roll on Uni when DS can get his own loans...