Opposition leader Simon Bridges says he's seen no evidence that his sister has been teaching creationism in place of the New Zealand science curriculum at a private christian school.
Mt Hobson Middle School is for students in years 7 to 10 and is run by the Villa Education Trust, which also operates two charter schools.
The school is being accused of using science classes to teach creationism as the preferred theory of how the world began.
The teacher at the centre of the allegations is the sister of Mr Bridges and wife of National MP Simon O'Connor.
A former student claims Rachel O'Connor played a video purporting to show science had found proof of God's existence.
The school said it received a low-level complaint from the student's mother at the time, which was dealt with in a conversation with her.
The complaint wasn't about religious education being taught, just that it shouldn't be part of science classes.
Given National Party leader Simon Bridges has aspirations to be the prime minister, he was asked whether he believes in evolution - he says he does.
When he was asked whether his sister believes in creationism, he responded, "look, I don't really care''.
"She's a New Zealander and she should be able to believe whatever she wants. What's important is this is a private christian school, it's entitled to have those views in New Zealand society but it also needs to teach the New Zealand curriculum and there's nothing to suggest it wasn't.''
Mr Bridges said he won't deign to ask his sister what she has been teaching because he said this is simply a political hit-job.
Villa Education Trust has also applied for its two charter schools, which teach christian values, to be incorporated into the state system as designated character schools - whether they're successful will be a decision made by Education Minister Chris Hipkins.
Mr Hipkins said there's only very narrow criteria for religious instruction in state schools - often in a lunchbreak outside of classroom hours.
"Creationism isn't appropriate for science classes in New Zealand,'' he said.
"It's not part of the New Zealand curriculum and I'd expect all schools to be teaching to the New Zealand curriculum.''
ACT leader David Seymour is the former under-secretary for education and is against the government's closure of charter schools, which were the result of a confidence and supply agreement between his party and National.
Mr Seymour said creationism is something children should be taught but it shouldn't be sold as the absolute truth and only world-view.
"Now if you teach a kid that the world was created in seven days by a man in the sky as gospel, then potentially they're not going to have respect for world views and they'll miss out on future opportunities.
"Now on the other hand, if you look at the Villa Education Trust curriculum it's actually one of the richest and most diverse curriculums I've seen,'' he said.
Mt Hobson Middle School's academic manager Alwyn Poole is standing by Mrs O'Connor's teachings and disagrees with the student's claims that creationism is taught as the preferred theory of evolution.
He said science teaching is based on profound discussion and reaches across broad disciplines.
Mr Poole said it's always been well advertised that the lines between its subjects are not black and white.