Oh, me too!
Comprehensive schools have had to / are learning rigour and accountability, and grammar schools are forgetting these vital elements. Not all of them, I hasten to add, but there are always those which are only grammar schools by name, but which still attract parents seduced by a pretty uniform and the word "grammar".
But- how do grammar schools add value? (That is, make sure their students exceed the expectations provided by the data.) They take in children with very high scores at 11, most of whom should, therefore, get high grades at 16. If they don't get these grades, then there is something intrinsically wrong with the system. Maybe it is over confidence, maybe - see above - a loss of rigour. Maybe it is to do with students' perception that they do not need to fight hard; a mixed comprehensive school would teach them, and their teachers, how to do that - how to strive!