The grammar school I went to was rather different than those around now. For a start, it had a primary school too. And all those who went to that carried on into the secondary part regardless of passing the 11 plus or not. The secondary side was larger though. First three years had 5 classes streamed on merit (A,B,C,D,E) with some moving either up or down. And some kids being transferred from a secondary modern if it became plain they'd failed the 11 plus wrongly, as it were. 4th form onwards was streamed by subject.
The beauty was you got a good social mix of kids based mainly on ability - rather than where they lived.