Schools say they are at "breaking point" as new figures show they are standing down a record number of students for assaulting teachers.
Latest Ministry of Education data show total stand-downs last year increased by just over 1000, or 8 per cent - the first increase on an age-standardised basis since the ministry started actively discouraging stand-downs a decade ago.
Physical assaults on other students and teachers accounted for 80 per cent of the increase.
Principals Federation president Whetu Cormick said schools could change policies to keep students in school after lesser offences, but most schools automatically stood students down after serious assaults.
"Schools have been working incredibly hard to engage with young families with children, and stand-downs and suspensions in the primary schools are often a last resort, but our colleagues are telling us they are at breaking point," he said.
Northland's Te Tai Tokerau Principals Association president Pat Newman recently threatened to suspend children indefinitely because of growing violence, with children throwing desks, fighting in the playground and stabbing other kids with scissors.
Northland has the second-highest overall stand-down rate of 32 for every 1000 students, just behind the West Coast (34). The national average rate is 20.6, up from 19.3 in 2015 on an age-standardised basis.
Stand-downs for assaults on other students jumped from 4.9 for every 1000 students in 2015 to 5.8 last year (about 4314 cases), the highest since 2012.
Stand-downs for assaults on teachers rose from 0.8 to 1.1 for every 1000 students (about 780 cases), the highest level on record and more than double the rate of 0.5 for every 1000 students in the early years of last decade.
Christchurch school counsellor Sarah Maindonald, who represents schools on the NZ Association of Counsellors, said children's violence reflected growing stresses on families.
"Students are generally under more stress. They have academic stress, and they have stress around the financial state of their families and housing," she said.
She said the removal of tagged funding for school counsellors in the 1990s meant most counsellors were now coping with higher numbers of students, leaving less time for preventative work and forcing counsellors to focus on crisis work.
"We are having to deal with a lot more issues that are precursors to mental health issues, and family violence," she said.
However, Secondary Principals Association president Michael Williams, principal of Pakuranga College, said he believed student violence was decreasing.
"Forty years ago children used to have fights at school. It was behind the bike sheds, there weren't videos of it," he said.
"The only reason we see them now is because of social media so they are publicised."
He said schools no longer tolerated bullying.
"Twenty years ago kids were told to harden up. Now we have excellent programmes around educating children about bullying and there is no tolerance of violence," he said.
He said schools needed disciplinary measures including stand-downs, which principals can impose for up to five school days without going to the board of trustees, and suspensions, which do need a board decision either to lift the suspension or expel the student.
"Stand-downs and suspensions are part of the tools that schools use. In both cases the students are coming back to school and in almost all cases the students go on to good outcomes," he said.
Suspensions increased only slightly last year, from 2616 to 2692, the first increase since 2009.
Students under 16 who were expelled from school but have to be accepted in another school ("exclusions") increased from 884 to 905, but students 16 and over who were expelled ("expulsions") dropped from 156 to 113.
Three-eighths of the 2692 students who were suspended were eventually excluded or expelled. Suspensions for the others were either extended (16 per cent) or ended (46 per cent).
Students in low-decile schools, boys and Maori students were three to five times more likely to be stood down, suspended, excluded and expelled.
Last year Maori students made up 45 per cent of all stand-downs, 51 per cent of suspensions and 53 per cent of exclusions, but only 33 per cent of expulsions.
A Ministry of Education spokesperson said all secondary schools still received funding for guidance counsellors of between 0.08 and 0.45 fulltime equivalents for each year level from Years 9 to 13, equating to 871 fulltime-equivalent counsellors last year.
However since the 1990s this funding has been added into each school's total funds for staffing, and schools have been free to decide how to use their whole staff funding allocations.