I am against selective education because I passed the 11+ and saw the alternative for my primary school friends who didn't. Anyone saying we should have more grammar schools should be honest enough to add: 'and we'll have secondary moderns for all the rest.'
It amazes me that some of the greatest fans of grammar schools are people who failed to get into them or would have done if they'd have taken the 11+. Maybe I'll write a PhD on the subject if I have the time.
My school had its fair share of poor teachers, bullies, underachievers, neurotic over achievers and mediocre students who worked very hard but were never going to trouble the top of the end of year exams. It's naive not to realise that. It's also naive to think your child has made it by passing the 11+. Getting in is not the end, but the start. You have to watch your child's progress like a hawk - and I'm not just talking about academic progress.
The mediocre students were bullied for being thick by some of the cleverer children and some teachers. I imagine they weren't thick - after all, they passed the 11+ - but but they were just thick compared to the rest of us. That's what happens when you encourage competition against others rather than achieving to your own best standard. Someone is always going to be bottom of the heap and ridiculed for it.
We also had streaming for English, Maths and Modern Languages. Those of us in the top set were encouraged to look down on the others. I think that's okay because we were really clever 
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You really didn't want to be in the third set because oddly, the duffest teachers who were coasting got those classes so those pupils struggled and floundered. The sensible thing to do would be to give those classes to the most gifted teachers, but no one smart has ever said grammar schools were sensible.