What I don't understand about selective grammar schools

[Hullygully]

is why, if all children follow the national curriculum and take GCSEs, you need to be "cleverer" than other children to go to one. Equally, why does it matter therefore, if children have been coached to get in? What am I missing?

Maybe you live in the same area as me, GiddyPickle, I moved here for the good comprehensives, but there are grammar schools that cream off the very top. However some of the very top don't even do the exam, for the very reasons you state. The local comprehensives regularly send DCs to top universities-every year there are pictures in the local paper of those who have got places at Oxford, Cambridge etc.
I actually prefer the fact that they just take the very best from a huge area-it leaves the comprehensives with a proper mix of abilities.

we are in the north and our grammar school spans a wide area over two counties

the kids DO mix some outside school but maybe not so much as they would otherwise do

the small number who come from our town 2 or 3 for each of my children - have naturally become their best mates .No problems socially. My kids not sporty so cannot talk about that but they do get involved in drama debating etc