This sound rather premature as my girls are only in year 2, but I have just returned from a parents evening. DD1 is 'average' for her age/year group and DD2 is working at year 4 level. DD2's teacher started going on about grammar schools but I really hate the idea of putting the girls in different secondary schools.
I know they still have 4 years to go and things may change, but I just wondered if anyone had experience of this and how it has worked. They are in different classes at primary school but they still all know each others friends and teachers and they spend so much time at home chatting about school, that I imagine them losing that closeness if they went to separate ones.