As always, it's only when you read comments about something you know a lot about that you realise how much mis-information is posted on these forums!
Yes, GHS parents are "rich" by any global standard, as are the parents of just about any fee-paying school in London. However, most parents are "normal" no private planes, no chauffeurs, etc. We ourselves walk to school; drive a 15-year-old car; cook our own meals; do not employ a nanny; fly EasyJet for holidays; etc etc and we and our children have been very happy at GHS. There is a thriving second-hand uniform shop, run by a lady whose daughter attended the school many years ago. Most parents buy uniforms there or get hand-me-downs from friends hence, you'll see many different tones of grey amongst the boys' shorts!
Xashax: the school most definitely prepares boys for 8+ and 7+ exams that is the main aim of a pre-prep. Some boys do stay on til 11 (or 10) for various reasons (mostly because their parents would like them to move to a boarding school at 11 or because they plan to move abroad -- so there's no point in their boys moving to a day prep school at 8.
Fireworks and babybarrister it is simply not true that "everyone" has a tutor. GHS prepares boys very well for the 7+ and 8+ (and girls for 11+). Some people employ tutors either because they've been told their children are border-line candidates for their chosen school or, more often, because they're insecure. But it is most definitely not necessary to have a tutor if your children are proceeding normally with the school curriculum. I know many children my own included -- who have gone on to very good prep schools without having been tutored.
Woodychip -- I don't know when you went to the summer fair but every year that I know of the summer fair has been on a Friday, not a Saturday. If you saw many nannies there it's probably because there are many two-career couples amongst the parents....
OP -- in case you're still interested: the selection process, from my observation, aims to identify children who have a bit of a "spark". They can't possibly look for academic ability at age 3 but they do like to see if a child takes interest in a story when it's read to him; if he can participate in a group activity; etc.
Finally, GHS is just a lovely and very nurturing school. The teachers are warm and friendly and take a keen interest in the children. Children are encouraged to be polite and kind to each other and are also encouraged to take an active interest in the world around them.The physical facilities are cramped compared with state schools but they are bright, well-maintained, full of beautiful art work (made by the children) and children are greeted by lovely music (from CDs) when they arrive in the morning.