NCEA examinations will begin next week, but tens of thousands of candidates are unlikely to turn up for them.
Principal and teacher groups say they are concerned that some students do not intend to sit the exams because they already have enough credits to pass.
For each of the past three years more than 50,000 students, or about 10% of those who should sit exams, have failed to turn up.
The Secondary Principals Association says that under the NCEA structure, many students, particularly those at Year 12 level, have already gained their Level Two certificate.
The Qualifications Authority says the 10% no-show rate is not much higher than day-to-day student absences.