"NZQA has said it is confident in the level the exam was set at. I have asked them to provide me with a full report on the matter."
This is the second year in a row that the authority has struck problems with maths exams. An independent review found that last-minute changes led to mistakes in four maths and statistics papers last year.
This year Middleton Grange School Year 11 student Evie Yeo sat a Level 2 internal maths exam as well and said it was easier than the Level 1 paper.
Kāpiti College head of maths Jake Wills, who is organising the open letter to NZQA, said some of the questions required material that was part of the curriculum at Level 2, not Level 1.
"It's not super-major. It's not like the issues we had last year where one of the questions was impossible, but for a national exam you would expect better," he said.
But NZQA deputy chief executive Kristine Kilkelly said the authority was still "confident in the quality of the Level 1 Mathematics examination".
"All NCEA assessments are aligned to the standard and the NZ Curriculum," she said.
"The Level 1 Mathematics examination was set by a team of experienced mathematics teachers, for the right curriculum level and is consistent with the specifications for the standard.
"Students may find some questions in examinations more difficult than others, especially those parts of the question aimed at excellence. Parts of the examination will be challenging, but students often do better than they expect."