A Wanganui High School teacher was threatened by a student with a knife last week.
The incident happened last Tuesday after classes had finished for the day.
Wanganui High School principal Garry Olver said the student confronted the teacher with a knife.
"Fortunately, the teacher's prompt defensive actions prevented anyone from being injured."
Mr Olver described it as a one-off incident and said the student was one with special circumstances.
"There is no reason to believe that this type of behaviour will be repeated."
He said there had been no witnesses to the incident and no one was injured. The student has been suspended from school.
Mr Olver said he understood the student was currently in a secure facility, while the teacher involved was on leave, but had visited the school yesterday.
He said the school was working with the police over the incident.
"Support measures have been put in place for both the teacher and their family, as well as for the student and their family."
Wanganui High School is Wanganui's biggest school, with about 1600 students and 160 staff.