The big difference between the state grammars and the independents (outside London area that is) is that the former "select" their pupils while the latter "recruit" them.
WGS for example will bend over backwards to arrange tours of the school, trial mornings etc. The state grammars like WGH and AGS have so many children applying they don't have to put in much effort to attract high calibre pupils.
Do you have a daughter/daughters at WGH?
Yeah, good point Resmum.
btw We have a large network of friends who send their loved ones to WGH