Selection at 11 or 14 indeed might indeed let down some children but they are being let down now, the question is which system lets down the least. I don't imagine any system will ever be perfect.
Children whose lives mean they are unable to focus on academic study - whether by intellect or circumstance the reality is they can't focus on academic study and should do something that will make a positive impact on their lives.
The kids who are simply late developers - We cant hold the rest back for a few late developers, if they really are late developers then they will just have to catch up. Isn't that called real life?
Those who are bright but have a passion for something vocational would be given an advantage by selection, they could develop their vocational skills to a high level and be as successful as any 'professional'.
No-one is suggesting a return to the old days of grammars and secondary moderns. It is possible to select for skills in a positive way and not just winners and losers. Academic study isn't for everyone and it isn't the panacea for a wonderful life. Most scientists get paid less than teachers and have worse pensions (sorry a personal comment there). Countries like Germany manage it and vocational schools are valued as much if not more than academic schools.
At the very least why are we pushing children who are not academic to stay in school until 18, and do A-Levels? A-Levels should most definitely be for academics and I think many of the comments in this thread are about children who shouldn't be doing them.
How about we stop so many children doing A-Levels and just teach them to read and write? And while we are at it way to many go to uni, its totally pointless.
ET - are you suggesting we ban selection by faith? stopping all Grammar schools? Closing all Private schools? I can see its possible but how do you stop selection by moving house to expensive area?