can I add my 2pence worth?
In italy children go to school at 6 but by then a large number have attended kidergarden for 3 yeras and a many have learnt to read by then even if it taught in a v. 'unofficial way'. (there's no curriculum for nurseries that says they have to teach to read).
SO I think the problem is not so much at whata ge you teach them, but mainly how.
DD,3, can recognise most letters of the alphabet, but we never set out to teach her (I'm definitely NOT that kind of mother), but she started asking and now she can link the letters to the names of people we know.
What I mean, is, I don't think it is necessarily bad that school starts so early, but the emphasis should be put on learning through play for the first few years, and definitely no exams until 11!!
The advantage of starting so early is that by 21 british students can be graduates and enter the workforce (and they WILL find a job).
In italy even if you're excelelnt, you don't graduate until 23/24 and then it might take you a couple of years before you find a decent job. And that's just a minority of people.
The fact that continental students seem to do better aftera while is probably more due to quality of teaching than the age when they start!