I haven't read all the thread so apologies if I'm repeating anyone here, but I wanted to offer my point of view.
I went to an all-girls grammar school and despite leaving school (with 10 GCSEs and 4 A Levels) 17 (ouch) years ago I still have "issues" that I can trace directly back to school.
I was one of the 'stupid' ones in my class, so I lost all confidence in my own abilities - something I've never quite overcome. I doubt myself all the time. In every school there are going to be kids that the teachers ignore and I was one of those unfortunately. On my last day, one of the teachers told me I was one of the girls she wouldn't remember because I wasn't very good and I wasn't very bad - doomed to a life of mediocrity!
What I'm trying to say is, that I think if I'd gone to a comprehensive school, with streaming (I thought they all streamed - perhaps not?) then I'd probably have been in the top or second set for everything, I'd have had more attention from teachers and I would have had more confidence in myself.
We recently moved back to the area I grew up in. I don't have a daughter, but if our new baby is a girl, I don't want her to go to my school.
So don't fall into the trap of thinking grammar schools are wonderful, because they're really, really not.