its soooo confusing, i wish all states named things the same.
here in victoria the cut off for primary school is to be 5 before mid-late april.
so we have
3yr old kinder-optonal
4yr old kinder-compulsary

primary school
prep
grade 1
grade 2
etc etc.. to grade 6

for us with DD2 being a feb baby she could go to 3 yr old kinder next year but we're holding her back so she will start prep/primary school in 2015

hope that helps