"But sometimes you've got to stand up for yourself, and if that means hitting somebody else, I don't have any issue with that."
Australian anti-bullying experts have condemned the similar message being promoted by Dr Demartini.
The doctor, who is on a lecture tour to promote his book Benefits of the Bully, has told Australian audiences a bullied child was "a by-product of over-support".
"You have to teach the child the truth. If you teach them a fantasy world where we are all meant to be nice and get along, they will not appreciate how life really is," Dr Demartini told news.com.au.
"If kids go out there and learn martial arts, learn how to be intelligent and have friends, bullies will drop off."
Mr Grant, who has authored eight top-selling parenting books with his wife Mary, said: "Life is tough. And you've got to stand up. And I think most bullies are cowards anyhow."
Secondary Principals' Association president Patrick Walsh said it was a dangerous message to send to students that you have the right to take the law into your own hands.
"All that does is import the law of the jungle into the school, where might is right and where violence becomes a justified means to solve your disputes."
However, Mr Walsh said there had been a shift within schools about how to deal with bullying, caused by a September Ombudsman's report into bullying at Hutt Valley High School.
The report found the school had not adequately dealt with several incidents in 2007, including a sex assault on a student and bullying and intimidation of teachers.
Mr Walsh said more emphasis was now put on developing resilience among victims, and ensuring they reported bullying and kept doing so until action was taken.
Associate professor in clinical psychology at the University of Auckland Dr Ian Lambie said any idea that violence could be a solution to violence was outdated.
"The key thing is for the school and the school board to have a zero tolerance on it ... it's how you deal with [bullies] from the leadership of the principal down."
BULLYING IN NZ
* Bullying in schools is more than 50 per cent above the international average, according to a report to a Ministry of Education summit in 2009.
* More than 6 per cent of students are bullied at least once a week.
* A 2007 report found a third of school students had threatened physical violence.