Keith, from personal experience with my own children, I really don't think it makes
that much difference now ... I do, however, believe it can make an enormous difference throughout the teen years.
The teen years are difficult enough times anyway and are even moreso for children whose hormones haven't kicked in yet and who are desperately trying to keep up with their hormone fuelled peers. And then you also get the legal age situations ... ie. driving a car, going to the pub. Those who were accelerated and are younger have to wait while their friends are all driving and/or going to the pub.
My son who is now 18 was accelerated just in maths from Grade 4. So while he was in Grade 4 he attended Maths classes in Grade 5 and whilst in Grade 5 attended Maths with the Grade 6'ers. Then when he got to Grade 6 they couldn't accelerate him into high school because their timetables were so different to the primary classes. He was apparently given advanced work to do, however, mostly he was left to his own devices. He totally lost interest in Maths in Grade 6 (even though his exam results were tops) and whilst his aptitude was there in his secondary years his earlier love for and exceptional talent in the subject just waned and he became a very average student.
For the second half of last year when my son and his mates were sometimes out at the pub on a Saturday night, my loungeroom usually contained from 2 to 4 of his friends, (watching tele and waiting for the others to come home), who couldn't go to the pub because they were too young (because we live centrally right in the middle of town our home was a bit of a drop in place for the young people).
As well, my son was judged by the kindergarten teacher to be more than ready to start school earlier than usual because in her words "he was more advanced than most of the students who had just completed kindergarten". And so, on her valued advice I started him early. Within two years he was having remedial work for his handwriting which was put down to the fact that he didn't spend long enough at pre-school where they do a lot of cutting, pasting and other craft type work to develop the fine motor skills.
It is my belief that all children develop differently at different stages and ages and then at some point they become responsible adults (well that is kind of the plan at least

). Some babies will walk quicker than others and more than often the others will have mastered language before the faster walkers. There are so many different ways in which a human grows and there really is not
any benchmark as to what happens when. An enormous number of people eke out a living telling us what should and shouldn't happen and when. Personally I do not believe in advancing a child. There are numerous ways we can stimulate a child whose interest and abilities are above those of his/her peers. What would be wrong with providing that stimulus whilst the child grows to continually shine in the class they are in. To me the very act of taking a child out of his current peer group and placing him in another must cause some stress to the child - socially and in regard to his perception of himself. Imagine being a little child and you are one of the smartest kids in the class and then next year you've had to leave your friends behind and start trying to get to know another group of little people and you're also just average in your work - like everyone else in your new class.