I live in a grammar-area town that until 3 years ago only had the 'left behind' comprehensive. Very few local children went there. If they failed the test (taken at age 10, not 11), they went to faith schools or private schools in distant towns.
Then we got a faith school that had a 50% cap on faith places and things started to look up for all the non-religious borderline kids, late starters, dyslexics and the ones who were ill on the day of the test.
When the state allows 100% faith places and grammar selection in your town, you will find that if your child is not selected, they are destined at the age of 10 to be a "follower", while their luckier friends train up to be "leaders".
If you support a selective system, you really should consider what you intend to do when someone you love is not selected to have a decent education. It is absolutely possible - I know so many intelligent children in my town who have fallen into the wrong group. It could have happened to Theresa May if she had been a bit under the weather on 11+ day.
Families who accept the non-academic local school see their kids emerge with A levels in soft subjects like graphics and drama. The school doesn't really do maths and science at A level due to lack of demand, which means no-one even tries to take them.
The only honest solution is to scrap selection (11+ and faith), and manage and fund ALL schools well so nobody wants to look for an escape from their local comp. London seems to be doing well, the faith schools seem to be doing well - both with all-ability intakes - so it can be done.