Boys as young as 8 are attending anger management courses as schools and social agencies struggle to cope with "P children" born during New Zealand's methamphetamine epidemic.
Auckland University psychologist Trecia Wouldes, who is studying 107 children born to mothers who used meth during pregnancy between 2006 and 2010, said the effects were showing up in early childhood centres and schools.
"When you talk to people at the coalface of childcare in South Auckland, I work with a lot of people doing early childhood intervention, and a lot of it is meth," she said.
"I gave a talk to Special Education [which serves early childhood and schools]. They said it used to be that the kids they saw were Down syndrome and other birth defects. Now it's all behavioural issues that are related to drug abuse and maternal mental illness."
West Auckland anti-violence agency Man Alive is taking 10 boys each term on a Boys Alive anger management programme for boys aged 8 to 12, who are referred from all over Auckland.
Operations manager Neil Brand said it was not uncommon for the boys to have been exposed to drugs such as methamphetamine ("P"), but most were also struggling with other issues such as family violence and parental break-up.
"Often anger is the presenting issue, but it's never the only thing," he said. "People don't just wake up one morning and smash the window."
The eight-week programme including a weekend camp helps boys to recognise when they are getting angry, builds up their self-esteem, and shows how they can influence the way people respond to them by their own behaviour.
"Ninety-nine times out of 100, if I hold my hand out to you, I'm going to influence you to shake my hand," he said.
Parental drug and alcohol use has jumped from around 42 per cent of children served by the national multi-agency High and Complex Needs Unit in each of the past few years to 62 per cent of the unit's 147 children in the nine months to March.
Those where mothers used drugs or alcohol during pregnancy have gone up from a third to almost half.
The increases come roughly a decade after the methamphetamine epidemic peaked at 2.7 per cent of New Zealanders aged 16 to 64 (70,000 users) in 2003, with a similar rate of 2.2 per cent (61,000) in 2007-08.
Usage has dropped to 0.9 per cent (25,000 users) in the two later health surveys completed in 2012 and 2013.
Dr Wouldes said her sample of mothers who used P were also struggling with multiple other problems.
Many were physically or sexually abused. More than half were solo mothers when they gave birth, two-thirds used alcohol and marijuana, and 88 per cent smoked cigarettes.
Their children have been slower to crawl and walk than the children of mothers who didn't use P, even after adjusting for all the other negative factors in their lives.
Child, Youth and Family's general manager of residential and high needs Nova Salomen said the High and Complex Needs Unit funded 74 teacher aides for high-needs children in the nine months to March, up from 55 in the previous year and 42 the year before that.
Ministry of Education manager Katrina Casey said teacher aides were funded for 1500 students in total last year, rising to 2125 in the financial year starting this July and 2750 a year after that.
She said there was "no evidence of an increase in the number of primary-aged children unable to attend primary school because of anger and violence issues".
Numbers being stood down, suspended and excluded because of violence have all declined over the past five years.