if child born in may 2011 when does he go reception

[LittleBlondeNinja]

If my son is born in may 2012 when do i apply for primary school? He is 3 this year and going to pre school in nursery on 3rd may so when do i apply for school?

You've put a different date in your title, from your OP.

If in England or Wales (Scotland is different, not sure about NI) then you go the September after you have turned 4.

So, if born in May 11, he will start school (Reception) Sept 15
If born May 12, he will start school(Reception) Sept 16

You apply in the Autumn of the year before they start - different Local Authorities have different dates the applications have to be in by, I think.