I don't think moving a child up a year does work - differentiation should be done within the year group. It's too complex otherwise - is the move permanent? Will the child therefore go to secondary school a year early? This has all sorts of ramifications - from having to travel on a bus alone at possibly just turned 10, to being the only one in the year not to be learning to drive, or being the only one not able to go to a 15 certificate film, or go to a pub to celebrate after A Levels. And it MATTERS to children to be able to conform to what their friends are doing.
DAL - I disagree with your assertion that 'acceleration is what is needed.' Remember acceleration is not the same as progress. For a child to make steady progress (and continue to learn new things), you do not need acceleration, you need forward momentum. Acceleration is the rate of increase of progress, and suggests that the rate of learning should be getting ever faster and faster. Rather than that progress should continue to be made, which is more sensible.
My biggest problem with this whole issue is the identification of a cohort of children to be labelled 'G&T'. Because I think that within a class, different children will excel in different areas, and thus the teacher should be able to give extension work as and when it's needed, not simply hand out harder work to the 'people on the register'. I've been pleased this year that ds1, who is Y4, and not on any G&T register has been given extension maths work when appropriate - he isn't even in the top maths group, but he finds some maths really easy, and on these occasions he's been stretched further. I'd be very unhappy if this didn't happen, simply because he wasn't in the 'identified group'. His class is a particularly high achieving class, (and would be in any school), the other class in the year is much less high achieving, and in that class he probably would be in the top maths group. However he is better at literacy based work, and is in the top literacy group. Still isn't 'labelled' as G&T though - probably because of some high achieving girls in that group, but he is still stretched.
Dd in Y2 is probably at this stage a 'higher achiever', and despite being the youngest in the class is probably the best or second best reader, top group for maths, probably the best writer in the class. To my knowledge she isn't on any G&T list either - but this doesn't mean she isn't challenged in class, or motivated to work. She went to bed last night with a couple of longish novels, and a piece of paper and a pen, so that she could write down any 'interesting' words that would be good for her to use in her writing. Wasn't my idea - was entirely hers - so she is stretching herself, which is the ideal imo!
Ds2 is going to struggle at school, because of a speech delay. He has however been assessed as being 98th centile in intelligence, so it will be interesting to see how that pans out. What he is going to need is extra language support, so that his abilities aren't hindered by a lack of language.
I think what I'm saying is that every single child is individual and has individual needs, and a crude 'register' identifying a cohort of children is never going to meet the needs of the whole class. And teachers get a lot of stick on here for not 'meeting the needs of the gifted', but they have to meet the needs of ALL the children, and for some children these will be complex.