The Secondary Principals' Council says an exam paper is sent to police forensic experts when there is a suspicion it has been altered after grading.
The latest NCEA annual report shows 299 reports of possible breaches of examination rules last year, one more than in 2013.
280 reports were substantiated, with the most common being a student bringing a cellphone into an exam.
Police said their document examination section had provided forensic expertise to the education sector, but an NZQA spokesperson said it only happened once last year.
Students found to have cheated were either given a warning or had their exam papers withheld.
Chair of the Secondary Principals' Council Allan Vester said some students had altered their exam paper before asking for it to be moderated.
"The forensics would be in a situation because students get their scripts returned to them, and then they can appeal the mark, which, as I understand it, it would mostly be around situations in which a student is found to have or believed to have changed their script."