Education Minister Chris Hipkins wants answers from the authority that oversees NCEA exams after there was an error in a maths question despite a "robust system to stop that happening".
A question in the Level 2 Mathematics and Statistics paper - which more than 34,000 students entered - asked students to work out the area of a section of a rectangle. But it was impossible to figure out.
New Zealand Qualifications Authority (NZQA) deputy chief executive of the assessment division, Kristine Kilkelly, confirmed the mistake to RNZ, 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.
But Hipkins says there is already a "pretty robust system" in place and wants answers from the authority.
"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 told The AM Show.
"NZQA do have to answer some questions about that because they have supposed to have put in place a pretty robust system to stop that happening."
Hipkins said he should receive a full report from NZQA in February, but is not sure how the mistake got past 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?"
But 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.
The Education Minister - who was filling in for the Prime Minister in her weekly media slot - also commented on accusations by the National Party on Saturday of "brainwashing" in a Level 3 English Exam.
Students sitting that test were asked to read a NZ Geographic article about water quality and the tension between farming and environmentalism, then analyse the linguistic methods used to explore change.
"An upwelling of public dismay has emerged over the parlous state of freshwater, particularly the pollution of favourite swimming holes," Kennedy Warne wrote in the article.
"Almost two-thirds of respondents regarded farming as the main culprit - more than double the number who held that view when the same survey was conducted in 2000."
That angered several National MPs who accused the qualifications authority of "state-sponsored bullying" and "brainwashing".
"There is a concern our kids are being convinced that farming drives environmental degradation," National's Agriculture spokesperson Todd Muller said in press release on Sunday.
"Farmers' confidence is at all-time lows, and this just adds to the pressure that is being heaped onto them by Government policy. They feel that anti-farming sentiment is becoming insidious in this country."
Hipkins said the question and text were appropriate.
"Absolutely... it is asking students to critique the various argumentative styles that are used in the writing, the rhetorical devices that are used in the writing," he said.
"That has always been part of the exam process. I think it would be very concerning if we got to the point where politicians were vetting material that went into a student exam."
Kilkelly told Newshub the question never asked the student to evaluate the text's content.