The bright kids who want to learn will find each other even if they are only 10% of the school. The obnoxious "don't wanna be there" brigade will find each other and bum along doing as little as possible for 4 years whilst the "top swots" crack on and speed ahead.
@Doncasterjan you say in your top post that your daughter is very academic - is there any possibility she could qualify for a local independent school on a scholarship based on brains and her aptitude etc?
When I was a child under 12 years old my parents were advised that my younger brother was academically gifted and that he would get into a private school on a scholarship if they (parents) wanted to pursue it. (My parents were borderline poor so they would have financially qualified for various bursaries and scholarships fir brain box brother.)
However .......
My parents decided against doing that because they didn't want to appear to be choosing unfairly for the brother. I was an average kid, and would not have passed 11 plus or any scholarships.
So my parents decided to send both me and brain box brother to the same local comp, in order to not split us up, to avoid favouring him, etc ..... and possibly also because it made it easier logistically to only have to do one school run to the same school etc.
My brother went thru the same comp school as me, met completely different set of friends, and got much higher grades and results due to his inherent aptitude for learning. He got:
10 x GCSES all A and A* grade
4 x A Levels
1 x AS Level
He went to uni and got a double first in Physics and Computer Science (not an Oxbridge type uni - a fairly average uni) but, again, he got a double first Science degree from "any old bog standard" uni - and probably achieved it with more ease and less pressure due to it not being a top university.
I got 5 x average grade O Levels, 2 x secretarial certificates and an office job at age 17. I never did have the brains or aptitude.
We both fared as well as we could have done in the comprehensive system.