Interesting discussion despite certain posters clearly hijacking the op’s thread.
The Kent style grammar system does seem problematic.
Selection at 11 in comprehensives is pretty common via setting. This is a more flexible approach which statistically leads to better overall outcomes. The 25 percent of pupils who would have been in a separate grammar have a similar experience being hived off into the upper sets of good comps which is why outcomes are nearly identical.
Most parents only care about how good a school is for their child. Good comprehensives have a huge housing price premium attached to them and are disproportionately used be the better off.
Any poster whose children go to a good comp who suggest they are making a moral sacrifice for other people is deluded and grandstanding. A sacrifice would be actively choosing to send your child to a failing school as a first choice so that you could get involved and turn it around.
However no one intentionally chooses a failing school because it goes against every aspect of human nature. Turning what should be a policy debate into one about personal morality of parents is completely spurious. Within an unfair system people aim to do what they can and not participating doesn’t make the system any fairer- only true political change can do that.
And what is unfair about the education system isn’t primarily what’s happening in Kent- it’s unequal access to good schools (mostly primary schools and comps) based on wealth. The gaps between the best and worst state schools is significantly more stark that the gap between the best state schools and grammar / independent schools.