"We are failing our kids," says Dr Jaimee Stuart, who has carried out research into bullying in New Zealand.
Her comments come as the 2015 Trends in Mathematics and Science Study (TIMSS) shows the country is once again among the worst in the world when it comes to bullying.
Among Year 5 science and maths students, 24 per cent said they were bullied on a weekly basis, with only 40 per cent saying they were "almost never" bullied.
•New Zealand pupils below average in maths
Only Bahrain and South Africa scored lower in this ranking than New Zealand.
The statistics improved slightly for Year 9 students, with 10 per cent of science and maths pupils in this year group saying they experienced some kind of bullying on a weekly basis, and 55 per cent saying they were almost never bullied.
This compares to 73 per cent of Irish Year 5 students who said they were almost never bullied, and 80 per cent of Japanese Year 9 students who said the same.
Stuart, who has launched a consulting firm Infer Consulting to advise schools on best practice approaches to tackling bullying, said New Zealand was consistently at the bottom of these tables.
"It's really sad that it continues to go on," she said, adding it was unfortunate that no progress had been made despite a lot of research.
New Zealand's "harden up, be tough" attitude to bullying was to blame, Stuart said, and the TIMSS results "should be taken seriously".
"We are failing our kids, and I think we're failing our kids by not implementing the right programmes and not focusing on positive social relationships for kids."
The focus had been on the concept of bullying, and not on what influenced it, or teaching children how to interact with each other in a positive manner, she said.
"That focus on holistic wellbeing has been missed and that's probably why nothing's been done about it."
Louise Green from the New Zealand Educational Institute said: "Children have the right to an education, that nurtures their full potential and is free from bullying and harassment."
Education Minister Hekia Parata said: "The longstanding issue of bullying remains an ugly and unwanted presence in our schools, but I am optimistic for the future."
A lot of work had been done since the study was carried out to address the issue of bullying in schools, she said, such as new guidelines on cyberbullying.