An error in an NCEA exam is likely to have thrown many students off their stride and impaired their performance, a high school maths teacher says.
The mistake in a table of figures made it impossible for students to answer a question in the one of three papers that made up yesterday's Level 3 statistics exam.
The Qualifications Authority said more than 12,000 students were scheduled to sit the exam and it apologised for the problem.
The co-head of maths at Kapiti College, Jake Wills, said students told him they were thrown by the mistake and found it hard to do the rest of the exam.
"My students were basically saying things to me like 'I felt like a failure', 'I felt like I couldn't do it' and 'what was I doing wrong?'," he said.
"They spent a large amount of trying to work out what they were doing wrong and that is another thing that will affect how they went in their other papers."
Students could choose to do the three papers in the exam in any order, and the stress caused by the mistake could have had a bad effect on those who chose to do the problem paper first, Mr Wills said.
"For some students, just over a third of the way into the exam they would have been going, 'I feel like I know nothing because this relatively straight-forward question is not working for me'."
Qualifications Authority deputy chief executive Kristine Kilkelly said it was sorry the error had slipped through its quality assurance processes.
"We are investigating to find out exactly how it occurred," she said.
NZQA was committed to ensuring no student was disadvantaged, Ms Kilkelly said.
"The examination papers will be marked as normal by the panel that has been made aware of the issue - they will take this into account when grading students work."