The New Zealand Qualifications Authority cancelled 23 students' results after finding them guilty of cheating in last year's NCEA exams.
The authority's annual NCEA report said 353 students broke exam rules in 2017, most of them by failing to follow instructions.
It said 10 students were guilty of dishonesty, including six who used their cell phones during an exam.
A further 11 students breached rules around authenticity or impersonation.
Sixty-three candidates hindered or influenced other candidates, 46 of them by talking to other students during their exam and 14 by causing a disturbance.
The report said 295 students failed to follow instructions. They included 117 who had a cell phone with them, 93 who had notes, and 11 who used or had inappropriate language or material.
The total number of exam rule breaches last year was the highest since 2012, when the authority found there were 354 breaches of exam rules.