Ten per cent of parents say they frequently smack their child, meaning if discipline is needed they turn to smacking more than half the time.

Children's Commissioner Andrew Becroft says there is no doubt the 2007 "anti-smacking" law change has worked to protect children.

His comments come after a report showing a third of Kiwi kids are still smacked by their parents.

Ten years on from the repeal of section 59 of the Crimes Act in 2007 – the "anti-smacking law" driven by MP Sue Bradford – which removed the defence of "reasonable force" for adults who smacked their children, a longitudinal study shows many parents still use physical discipline as a form of punishment.

WAYNE DROUGHT Then-MP Sue Bradford was the driving force behind the "anti-smacking law".

The University of Auckland's study Growing up in New Zealand has released its Now We Are Four report which reveals worrying statistics happening behind closed doors in New Zealand homes.

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The report showed a third of mothers used smacking as a form of punishment and regularly shouted at their children. One in 10 parents said they frequently smacked their children.

Three per cent of Kiwi kids regularly witnessed arguments between their parents which included physical violence.

One in every 12 mothers reported "exploding with anger" at their children frequently.

Before he became children's commissioner, Becroft was the country's Principal Youth Court Judge.

He said some of the cases which passed under section 59 before the law change could only be described as beating. "Even the law as it is does not require police to prosecute when the smacking is considered inconsequential. But what I do stand by is that there are more appropriate ways to enforce boundaries and to provide guidance.

"I think all parents know deep down there are better ways. There are good strategies and help that can be available for any parents...but I think there's a significant challenge in New Zealand for us to do better for our families," he said.

Becroft said many of the statistics in which New Zealand needed to improve - such as bullying, abuse and violence - could be traced back to family life and the home environment.

As a parent he said he knew there were times when all parents fell short and felt ashamed. "All parents love their children. Parenting is an inherently stressful business... the bottom line is we can do significantly better and we want to do better."

Shine client services manager Jill Proudfoot said a small smack as a form of discipline could often lead to more intense violence. "There's a continuum of violence that starts with a little smack and escalates. If they continue defying you then you have to hit harder and harder and do more serious things to control them."

She said physical discipline was strongly entrenched in New Zealand culture and while the change in legislation had helped, more resourcing was needed to support families towards better parenting practices.

The children who were witnessing domestic violence between their parents were reported as a small group, but Proudfoot said through her work she knew children often were more aware than their parents knew.

Children who grew up being hit and witnessing violence at home often had lower confidence, feelings of hopelessness, eating disorders, issues with lashing out and thoughts of youth suicide, Proudfoot said. "It's like children in war zones, they don't know where their safety is."

She said while there was no excuse for violent parenting, life stresses such as housing pressure, financial pressure and separation from children at a young age could all contribute to a parent who was more likely to hit their children.

Shine is a national domestic abuse charity and Proudfoot said the violence she saw in hundreds and hundreds of Kiwi homes was extreme. "Homicide rates are high but the number of near-misses is astronomical."

Separate research from the Brainwave Trust, an independent research charity, shows physical discipline may bring about immediate compliance from a child but it is shown to be harmful and is associated with a range of negative outcomes.

Growing up in New Zealand director Susan Morton said it was important to acknowledge how hard parenting could be for the current generation of parents who were dealing with a great many stresses in general life as well.

Justice Minister Amy Adams said recently that the Government would take action on New Zealand's appalling family violence record.

She said that New Zealand topped "the world at the rate in which we beat our partners and kids. We have the highest rates of family violence in the developed world.

"This is a shameful record."