The Wanganui schoolgirl beaten until she fell unconscious has not yet returned to school, nearly a month after the vicious attack which was caught on film.

The teenager says she still does not feel safe in going back to classes.

The attack, for which the bully was expelled and is now facing criminal charges, has prompted Prime Minister John Key to call for a review of anti-bullying policies in schools.

He has also asked Education Minister Anne Tolley to write to all boards to remind them of their responsibilities in keeping students safe.

But the school at the centre of the case says it has anti-bullying measures and its board is well aware of its responsibilities.

Wanganui Girls College deputy principal Maartje Morton said the school had zero tolerance for bullying, but the incident in which 15-year-old Robin de Jong was violently attacked on the way home from school was more than that.

"As soon as we know about it we do something about it," she said.

"But this is more than bullying, it is assault ... I don't know how we are going to change the attitudes that condone that kind of behaviour."

Mrs Morton said the school introduced an anti-bullying programme last year and had been making a "really big push" to emphasise that bullying was not acceptable.

"We always have, we've prided ourselves that we were a 'telling school' - that we have encouraged the students to tell us if they are being bullied and we act on it as promptly as we possibly can."

She wasn't sure what more could be done, but the school would review what had happened and continue trying to make it as safe as possible.

The education union NZEI said the Prime Minister was misguided in thinking that schools alone could stop bullying, as the root cause often lay well beyond the classroom.

"The Government is naive to think just writing letters to schools demanding they review their anti-bullying policies will make the problem go away," said president Ian Leckie.

"The causes of bullying are complex and often reflect wider social issues. Parents, whanau and the wider community have a huge role to play in identifying bullying and changing behaviours."

Labour's acting education spokesman David Shearer said writing to schools was "a useless way of making a difference".

"If they want to get rid of bullying they will have to take on some tough and complex problems - including getting tougher on intervening with the families of bad kids and with bad parents."

Children's Commissioner John Angus said no New Zealand school was immune from bullying. He agreed with Mr Key that it was a major problem that required an immediate response.

"While there needs to be a distinction made between isolated incidents of violent assault and ongoing bullying, both are best addressed by involving students in a whole school approach."

Mr Angus said research showed that schools that improved their overall culture and attitude to bullying and violence had more success in turning things around than those with intermittent or isolated programmes.

A 2009 research report by the commissioner's office said most incidents of bullying and violence happened without teachers being aware of them.