In the past, I've bought school shoes early in the summer holidays, and they've been too small by September.
Last year I left it to the last 2 weeks of August, and there was nothing left!
Both DC need new shoes -they've worn out. DS(14) is in a size 14 - he'll get whatever fits! DD(11) is probably now in an 8 - so it may well also be a case of whatever fits. Both have narrow feet, so DMs no good.