More than a third of 8-year-olds in New Zealand said they had been bullied in the last year, according to the largest study of child development in the country.
The findings reaffirmed New Zealand's ranking as one of the worst developed countries in the world for bullying and were described as "shameful" by the Children's Commissioner.
It comes as the Ministry of Education begins new work to understand how schools with low bullying rates have tackled the problem, and whether their policies could be applied more broadly.
The Growing Up in New Zealand longitudinal study, which has tracked 6000 children since they were in the womb, has previously shown that bullying was emerging very early in life.
At 4 years old, mothers of the children had reported that a third (36 per cent) of them were bullied.
"We were really shocked by that, firstly," said the study's director Professor Susan Morton. "But also were were asking ourselves 'Is this just the mums reporting that?'"
At 8 years old, the children were interviewed for the first time.
"We asked in a number of ways. It's not just 'Are you bullied?' It's getting at what bullying is in many ways. And still, shockingly, we are seeing 35 per cent of the children themselves reporting regular bullying at 8.
"We can no longer write it off as mums and dads being concerned about their particular children. This is the children telling us in their own words that this is happening."
The study noted that bullying was increasingly seen as a public health issue, and that children who were frequently bullied reported high levels of depression and suicidal ideation.
In all, 15 per cent of the 6000 children said the bullying occurred once or twice a year. But 14 per cent said it occurred weekly. Most of the bullying was categorised as "being put down or teased", and 12 per cent of the children said they were physically bullied at least once a week.
Māori, Pacific, and Asian kids were more likely to be bullied than Pakeha kids, as were children who did not identify strictly as a boy or girl.
Children's Commissioner Andrew Becroft, who has called for a greater focus on bullying of young people, said the findings were "perplexing" and "shameful".
"We need to redouble our efforts, both to work with people who bully and those who are bullied," he told the Herald.
Becroft and Race Relations Commissioner Meng Foon last year called for mandatory reporting of bullying in schools and for all schools to adopt evidence-based policies to combat bullying.
He is now working with the Ministry of Education to analyse schools and kura with low bullying rates and check if there were common threads between them which could be applied more broadly across the country.
More than 50 schools have adopted the Finnish project called KiVa, which claims to have reduced bullying by 42 per cent in schools where it had run for three years. But the ministry is trying to find New Zealand-based solutions which work for Kiwi kids.
Andrea Schollmann, the ministry's Deputy Secretary Education System Policy, said the anti-bullying work was ongoing and its findings would be shared when it was completed. She could not name the schools the ministry was working with, saying they had agreed to keep the work anonymous.
The Growing Up in NZ study also found that 10 per cent of New Zealand children were living in material hardship, and that disadvantaged children were more likely to be bullied.
But Becroft said bullying could not be causally related to poverty and disadvantage, and that it affected all schools, including wealthy ones.
"There are complex forces at play, that are often to do with intergenerational violence, of family modelling, and in New Zealand, I think, of a rather too lax view about the insidious nature of bullying and what it does to children and young people."