A New Zealand primary school has reported a drop in vandalism, serious injuries and bullying after abandoning playground rules as part of a university study.

Fairfax NZ News reported that two years after signing up to a study by Auckland University of Technology and Otago University, Auckland's Swanson Primary School no longer required a "timeout area" or as many teachers on patrol due to a fall in misbehaviour.

"We want kids to be safe and to look after them, but we end up wrapping them in cotton wool when in fact they should be able to fall over,'' said the school's principal Bruce McLachlan.

"The kids were motivated, busy and engaged. In my experience, the time children get into trouble is when they are not busy, motivated and engaged. It's during that time they bully other kids, graffiti or wreck things around the school,'' he said.

AUT professor of public health Grant Schofield said: "The great paradox of cotton-woolling children is it's more dangerous in the long-run."

He said society's obsession with protecting children ignores the benefits of risk-taking.

Children develop the frontal lobe of their brain when taking risks, meaning they work out consequences Mr Schofield told Fairfax NZ News. "You can't teach them that. They have to learn risk on their own terms. It doesn't develop by watching TV, they have to get out there."