A teachers union is calling for clarity from the Education Minister over plans to shake-up sex education guidelines

National has agreed with New Zealand First to scrap and replace gender, sexuality and relationship-based guidance for schools.

But the Post Primary Teachers' Association says no valid explanation has been put forward for the change or what it will look like.

Acting president Chris Abercrombie says it's not how schools work.

He says schools are putting in place now arrangements for next year, and any changes need to be made and communicated soon.

Minister Erica Stanford was not available for comment.