Violence, abuse and dangerous behaviour by students sparked more than 500 stand-downs, suspensions and permanent student dismissals in Northland schools this year.
Education Ministry figures released to the Northern Advocate show most were due to physical assaults on staff and students.
In total 311 violent incidents resulted in disciplinary cases in the year to October 16. Fifteen students, of whom 12 were aged under 16, had to leave school permanently as a result.
Figures are for schools in the Far North, Whangarei and Kaipara districts.
Tauraroa Area School principal Grant Burns said any violence in schools was unacceptable. "There is a real resolve among Northland schools to make schools as safe as possible and let as few kids slip through the cracks."
Mr Burns, who is also the outgoing chairman of the Northland Secondary School Principals' Association, said violence and bullying offences had dropped in recent years.
"I believe there is actually a lot less tolerance for violence in schools these days. It used to be that bullying was a rite of passage when students entered third form. Now, we don't tolerate it and steps are taken."
About two months ago a video showing a Ruawai College student being beaten up by classmates was posted online.
The 14-year-old was attacked in the school bathrooms while a group of students looked on and filmed. Two students, aged 15 and 16, were thrown out of the college.
However, the figures reveal a fall in disciplinary cases for violent and dangerous behaviour in Northland schools during the past four years - including a 24 per cent drop since 2011.
Schools had to make tough decisions where serious violence was involved, Mr Burns said. Removing a student was the last resort, but the safety of all students and staff had to be considered. Social networking sites and texting had created more problems. "We are noticing that online behaviour, especially through Facebook, is a major contributor to conflict in our schools."
Nationally violent and harmful-behaviour offences accounted for more than half of all student stand-downs, suspensions and permanent dismissals from primary and secondary schools this year.
Of the 17,558 disciplinary cases, nearly 9000 were for violence, abuse, dangerous behaviour or weapons offences.
In the Bay of Plenty there were more than 200 disciplinary cases for violent or dangerous behaviour this year, and 390 in Hawke's Bay.
New Zealand Principals' Federation president Paul Drummond said removing pupils from school was a last resort. Many schools had programmes aimed at promoting positive learning cultures and discouraging anti-social behaviour.
Student disciplinary cases for violence and dangerous behaviour had dropped significantly in recent years, down 30 per cent since 2009. But the decline might not necessarily correlate to less violence in schools, Mr Drummond cautioned. "Schools have put a lot of resources into managing serious behaviour and whether or not that's reflective of a decrease in anti-social behaviour outside the school gate - I just don't know.
"There are still obviously instances of serious misconduct that are challenging to manage."
Many violence offences involved male students in their intermediate and early high school years, Mr Drummond said.
"Just by their normal maturation they are starting to challenge and it's also a time when some children are starting to be disengaged from school.
"Risk taking of adolescents can be connected to that but some of it is also environmental reasons and the social environment they are in."
Sadly, violence among primary school students was not uncommon either, he said. "Reasons for that behaviour are complex."
Dysfunctional families, psychological and physical abuse, and problems with alcohol and drugs were often at play, Mr Drummond said.
Post Primary Teachers' Association president Robin Duff said some schools were reluctant to impose disciplinary action against students or report them to the ministry. They feared being judged by parents on the number of violent incidents that occurred.
"There is some pressure on principals and boards to keep it [violent and dangerous incident reporting] in-house."