Principals and teachers are backing the Education Review Office's call for national action on violent and disruptive behaviour in schools.
Half of teachers surveyed by the office in a report out on Thursday, said disruptive behaviour had become worse in the past two years.
A quarter of principals said they had seen students physically harm others, and damage or take property, at least every day.
The schools' watchdog said the situation was so serious it warranted a national approach, and the Minister of Education Erica Stanford said the government was "taking action" to turn around the behaviour.
The president of the New Zealand Educational Institute Te Riu Roa, Mark Potter said teachers felt vindicated by the ERO report.
"The experience that they're having in the classroom has been changing for quite some time and children are presenting with more and more complex needs and therefore some very difficult behaviours to manage and navigate in the classrooms," he said.
Potter said there were many reasons why more children were misbehaving.
"Some of it may be around a disorder or diagnosed need that they have. There's a lot that's coming as a result of the social dislocation that's happening economically in our country, the growing gap between the haves and the have-nots.
"So there's a variety of reasons at play and we don't want to be saying it's just about naughty children because children act out when something's not right and children in New Zealand are under pressure and we need to do something about that," he said.
Potter said schools needed more time and support to deal with the most difficult children.
"The problem we're facing with the behaviours presenting in classrooms will not be fixed just by teachers getting a bit of training and them being firm. I can tell you there are plenty of teachers being as firm as they can but children that they are dealing with just don't see those boundaries, they don't see those consequences," he said.
Potter said one-off training sessions or visits from experts were not enough to help schools and teachers improve children's behaviour and ultimately the system needed more funding.
'Schools aren't therapy clinics'
The president of the Secondary Principals' Association, Papatoetoe High School Principal Vaughan Couillault said about 5 percent of students were acutely badly behaved, causing harm to themselves, property or others.
He said schools needed more expert help to deal with those students.
"Schools aren't therapy clinics. We don't have a whole lot of psychologists running around in all of our schools and we don't have a whole lot of high-end behaviour therapists. Getting access to learner support at the medium to high level is really challenging and it needs to be resourced more appropriately," he said.
Couillault said bad behaviour was particularly prevalent among younger secondary school students whose primary or intermediate schooling had been disrupted by Covid-19 lockdowns and disruption.
He said a national effort to improve children's behaviour would be useful because the problem did not come from schools themselves.
"Schools don't teach that anti-social behaviour. They're not learning the fighting and the stealing and the swearing at grown-ups in schools, that's not actively taught. They might be seeing it from some of their friends, but where's that behaviour coming from," he said.
Marlborough Boys' College principal John Kendal said some students acted out because they were hiding learning problems.
"A lot of those behaviours come back to masking other problems. If you're reading at a five to six-year-old level in a Year 9 class, that's challenging so you try to mask and survive through a lesson," he said.
Kendal said it was hard to attract and keep teachers when the challenges they faced in the classroom were increasing.