More students are being stood down or kicked out of schools for fighting and assault, as schools struggle to cope with children of P-addicted parents and social problems like fetal alcohol syndrome.
An expert also warns that half of all students being expelled or excluded from school are on the autism spectrum, and noisy multi-teacher classrooms might be partly to blame.
After falling for a decade up to 2015, the rates of stand-downs, suspensions and exclusions from schools have all risen again in each of the past two years.
The main cause is physical assaults on other students, which have jumped from 4.9 stand-downs for every 1000 students in 2015 to 7.2 per 1000 last year, the highest rate since 2006.
Post Primary Teachers Association president Jack Boyle said violence and fighting which might once have been hidden, such as a brawl last week at Papakura's Rosehill College, were now being posted on social media where school principals could not ignore them.
Principals' Federation president Whetu Cormick said principals were being forced to stand down or excluded students because they were not getting the funds they needed to employ extra teacher aides, psychologists and other specialists.
"An increasing number of challenging young people are coming into our schools - P-affected babies and fetal alcohol syndrome," he said. "School leaders have been telling me they can't cope because they haven't got enough money."
Secondary Principals Association vice-president Deidre Shea said schools were seeing the consequences of insecure housing and health.
"If you are not well housed, and you haven't got good health support, then things are more likely to go awry for you," she said.
Ōtāngarei School's Myles Ferris, who heads the Māori principals' association Te Akatea, said high anxiety levels at home and at school made students highly strung "so that at any sort of provocation they lash out".
"I have had situations at school where teachers are getting hit," he said.
"These are kids and it's not their fault. They have often got conditions of fetal alcohol syndrome, autism and a whole range of differences, and P babies."
Autism NZ chief executive Dane Dougan said about 50 per cent of students being kicked out of schools were on the autism spectrum, and noisy multi-teacher classrooms might be to blame.
"That increase [in suspensions] directly correlates with when Modern Learning Environments started to be rolled out," he said.
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A Palmerston North couple is angry that their son, aged 16, has been suspended from a local high school for the rest of the year after offering a small packet of cannabis to two classmates last month.
The parents, who declined to be named to protect their son, said he was given the cannabis by a friend and did not understand the impact of taking it to school, apparently wanting to look "cool".
The principal's report to the board of trustees said: "[The student] has difficulty processing information and is easily led. His ability to make decisions is hampered by his learning disability. This incident is certainly out of character ."
But the board suspended the boy for six months and directed him to attend "an approved tertiary course" or an alternative education centre.
The alternative education centre said he was ineligible because it caters for ages 13 to 15, and arranged for him to attend another college. But the parents refused to buy a new uniform and disrupt their son's routine for six months, so he now stays at home alone while his parents work.
"He's such a routine boy, he's always up at 7am. Being out of routine is killing him," his mother said.
His father, who helped coach his son's school rugby team until his son was suspended, said he believed in consequences for actions, but they should be "reasonable".
"I understand consequences 100 per cent. But I also understand that school for young boys is also good, and that's what he needs," the father said.
"It's just so narrow-minded really. The statistics are there - male Māori boys are getting kicked out of school left, right and centre."
More than 5 per cent of Māori boys (57 per 1000) were stood down by their schools last year, compared with 4 per cent of Pacific boys, 3 per cent of European boys and below 1 per cent of Asian boys. Girls' stand-down rates were much lower in all groups.
Ferris said Māori principals wanted a law change to stop state schools excluding any child.
"I firmly believe that we should not be able to remove a student from school. What we can do is remove them from the vicinity of other students," he said.
"The Ministry of Education has a responsibility to ensure that all schools get the support they need to be able to manage their students."
Ministry deputy secretary Katrina Casey said the ministry was expanding its behaviour services to reach an extra 1000 children aged up to 8 each year. She said shared teaching spaces must have "sensitivity to individual differences".
The Palmerston North school which suspended the student for six months said: "Disciplinary hearings are confidential and therefore it is not appropriate to make any comment."