I have friends moving over from Spain next year and their DC are at primary school age.
Two of them were born in December and in Spain they start in the September of the calendar year they attain age 5. So in Spain if your birthday is between Sept-Dec, you start school a year eariler.
According to their dates of birthday, the DC will be going into Y1 & Y6 in Sept 2012 in the UK. But they are in fact already starting this year in Sept 2011 in Spain. My friends were wondering if they could enter school in the UK in the year above.