Thousands of teenagers in Auckland, Northland and parts of Waikato are skipping their NCEA exams.
They are making the most of a rule that means they will automatically get an unexpected event grade (UEG) for any exams they miss.
The Qualifications Authority said average attendance in the three regions during the first four days of exams two weeks ago was 55 per cent, well below last year's national average of 86 per cent.
Principals in the eligible regions told RNZ attendance at their schools ranged from just 15 per cent to about 80 per cent depending on the exam.
They shared their figures on the condition that their schools would not be identified.
"Today, for example there should have been 54 for English, and eight have showed. Last week for maths there should have been 31 and six turned up," said one principal.
"It ranges from some exams having nearly 50 per cent absent to some exams with less than 20 per cent absent. Within the exam, I don't know if they are completing every achievement standard and we won't know that until results are posted," said another.
Several principals told RNZ only about 20-25 per cent of eligible students were attending exams.
One said attendance varied widely between subjects but was averaging 45 per cent at their school and another noted that exam attendance was higher among Year 11 students than among Y12-13 students.
The principals told RNZ they were not surprised many students were opting not to sit their exams.
They said students who received an excellence in an unexpected event grade could not improve on that by sitting the exam.
One principal said academically-able students who wanted to improve their grades to merit or excellence were more likely to sit their exams than other students who were happy with achieved grades from their UEGs.
Another said the unexpected event grades were rigorous and a lot of hard work had gone into determining each students' grades.
The principal said living under a level 3 lockdown had created a lot of stress for many families and it was little wonder some teenagers were choosing not to sit their exams.
"They've done the hard yards, they're nervous, they're anxious and a lot of them are putting food on the table for their families," the principal said.
Another principal said they were happy that fewer students were attending exams because it reduced the risk of a Covid-19 outbreak.
Education Minister Chris Hipkins said the changes to NCEA were intended to give students a fair opportunity to attain the qualification, despite the disruption they had faced.
"For students who have experienced the most disruption - particularly those in Auckland - UEGs allow them to focus on achieving their best, while ensuring that support is there if they need it.
"I am confident students who have worked hard throughout the year will get the results they deserve heading into next year - whether that's school or on to further education, training or into work."