Hi Monica,
There was a time not long ago, when I could have put up a clear link to the school terms in NZ, but it looks like they're having a muck about with them from next year to allow schools greater flexibility in choosing their own terms times. Take a look at
this for some idea of how it works.
This tells you a bit about
enrolling kids into school .
I'll throw this link in as well just for good measure. It's about
Schooling in NZ .
Having posted all this, I'm wondering, by 'senior schooling', whether you mean colleges or unis rather than schools? Maybe I got it wrong?