A shocking loophole in the assessment system means more than a third of students could be leaving school with incorrect grades.
An "appalling" lack of moderation of internally-assessed work means teachers can boost grades, pushing up pass rates - and a school's reputation - without fear of being caught.
The
Herald on Sunday has obtained documents showing massive discrepancies between grades given out by teachers and the grades NZQA moderators awarded the same work.
Overall, 29 per cent of marking checked last year was found to be incorrect. The previous year, 27 per cent was incorrect.
Teachers and principals said the system was "open to abuse".
Rory Barrett, head of maths at Maclean's College in Auckland, said "I'm not saying we do it [grade boosting] here. But you'd have to be an idiot not to.
"If I wanted to, I could get my cat through just about any internal unit standard. They're not going to check."
Brent Lewis, principal of Avondale College in Auckland, said most teachers would mark professionally. But the system gave schools a lot of freedom and the anomalies created huge injustices.
"Career paths and life opportunities are being shaped by these decisions ... this is a critical issue."
Karen Poutasi, chief executive of the national qualifications authority, said the discrepancies were evidence that schools were doing as they were asked and submitting "borderline" papers for checking. She said it was the responsibility of schools to change grades once they had been moderated. However, principals said that never happened.
Statistics showed that every year more schools and students were taking advantage of the "slack" internal assessment scheme, in which only 3.2 per cent of teachers' marking was checked. Students were able to go through school without ever sitting an externally-assessed test - last year, 1224 attained NCEA based on internal grades alone.
Ms Poutasi said one incorrectly marked grade would not be "fundamentally problematic" to students.
Students said they would often choose to take internally-assessed subjects over those with exams.
One teenager said it was simple to "scam the system".
