Education Minister Chris Hipkins is demanding answers from the authority in charge of NCEA exams following a curly maths question which prompted dozens of complaints.
More than 34,000 students who took the Level 2 Mathematics and Statistics paper were asked to work out the area of a section of a rectangle.
But even a university maths professor said it was impossible and those who put the test together had "messed up".
Today, Hipkins told The AM Show he was concerned that there was a mistake in the exam despite a "robust system" to stop that from happening.
"I am concerned that there was a mistake in the exam after there were some issues in 2016 when they did a pretty comprehensive review of math exams, in particular, and they put some new systems in place which should have picked this up," he said.
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He said New Zealand Qualifications Authority (NZQA) was not sure how the mistake happened as all exam papers get past through several groups of experts.
"They have a panel that puts the papers together. It is made up of expert maths teachers and they do have technical experts that are supposed to review them. They have a small panel that is supposed to sit the exams beforehand to test them, to make sure there aren't any issues with them.
"My real question to NZQA, and I think it is everybody's question, is if all of those things were happening, how did this question get through?:
NZQA deputy chief executive of the assessment division, Kristine Kilkelly, has confirmed the mistake but said to identify the error, students would "have had to complete working which markers will be able to consider".
"Those workings will have demonstrated [the Excellence grade] to the markers, so we do not expect any students will be disadvantaged".
She also promised to review NZQA's quality assurance procedures.
Hipkins agreed with Kilkelly that if students had attempted the question and showed their working, markers would be able to see their level of skill.
NZQA said there were 34,465 students entered for Level 2 Mathematics and Statistics paper.
Dr Padraic Bartlett, a professional teaching fellow at the University of Auckland, said the problem had a couple of fish-hooks.
"One is that when you solve the problem you get something that is geometrically impossible.
"That is going to be a problem for really clever kids who are going to try and solve the problem and feel like it's impossible and then they're going to go back and check their working three or four times - that's going to be tough on them."
He said the way the diagram was written out was also misleading.
"I think that a lot of students are going to make an algebraic mistake here and it makes the problem much harder.
"If you're trying to test teenager's understandings you don't label it like that - I don't think it's intentional, I think they just messed up."