As someone who went to one, I must say I'm dead against grammar schools. I would support other selective schools such as technical or art schools.
My own experience (and others if you read the many forums) of grammar schools is that they were incredibly divisive and only really benefited the middle classes. I was an 11+ kid (theoretically intelligent

) but why was I, along with all the other 11+ kids in the bottom form? I'm afraid money talks!