Some teachers are so afraid of being labelled incompetent they are failing to report threats and abuse from students, says the secondary teachers' union.
A report to be presented to the Post-Primary Teachers' Association conference next week says teachers are increasingly facing students with severe behavioural difficulties.
Some schools have
hired guards and there have been several high-profile incidents this year, including a Alfriston College teacher punched so hard she needed hospital treatment for facial injuries.
At Waitakere College a 13-year-old boy was stabbed "down to the bone" and the schools sports co-ordinator twice had to break up the fight.
In both cases the police were called. But the new report, Managing Challenging Student Behaviour, suggests violence in some schools is going un-reported.
It says that teachers in some schools are working under a "climate of denial".
In those schools, the usual response of leaders was to blame the teacher, which in turn pressured staff not to refer incidents, or to attempt to deal with them on their own.
The report warns that some teachers may subtly or unsubtly encourage badly behaved students to stay away from the class.
"If this becomes the automatic response of school leadership, it can only be read as a climate of denial that cannot be in the best interests of student learning."
Chris Haines, president of the School Trustees Association, said teachers should go to their principal and, if they were not helped, could approach the board.
"Then it becomes a matter of the performance of the principal," Mr Haines said. "It's their responsibility to manage the school and boards will watch them to make sure they do it."
Secondary Principals' Association head Graham Young said schools needed an open environment. "The 'hide everything in a cupboard' mentality does not belong today. If it exists it is very, very disappointing."
Mr Young said on the whole students were better behaved today than 20 years ago.
"But what we do have are gross behavioural disorders which were not in the classroom 20 years ago because other agencies dealt with them. If they are now the responsibility of schools, is the cheque in the mail?"
The PPTA also says that schools are increasingly serving trespass orders against abusive parents.
In May, the Government announced a $10 million package to combat disruptive classroom behaviour and bullying. The report said that was an admission that schools were struggling to deal with difficult student behaviour.
