Bit of a daft question I know, 'cos the proper amswer is 'whatever fits them'!
But what I mean is, is there a kind of 'overlap' period i.e. could a pair of size 10s just be becoming tight, when you move to an 11, which probably has a fair amount of 'room for growth', or would you always go for the 10 1/2 in between?
I only ask 'cos the DSs have to have so many different pairs of shoes/ boots etc:
school shoes
plimsolls (leave at school)
trainers (ideally leave at school)
football boots (leave at school)
rugby boots - weekend
casual shoes/ trainers for home
that it seems mad to be just buying new pairs every time they go up a 1/2 size?
Also there seems to be huge variation in what still fits them at any time e.g. DS1 is wearing size 10.5 trainers, 11 school shoes, 11.5 football boots, and yet they all seem to 'fit' OK??