A group of Feilding schoolboys have been reprimanded after a nude image of a girl at school was shared.

A Manawatu school principal has called a group of boys predators after they were caught with nude images of a friend's ex-partner.

Feilding High School principal Roger Menzies called an assembly with the junior school students in November to address a "widespread" issue of students sending explicit images.

His comments made during the assembly have upset some parents who say he went too far and was creating mistrust between the sexes.

"I did say some boys are predators and they are. And the end game is sex and once they've had the sex they move on to someone else," Menzies said.

"Back in the day it was a dirty magazine ... now it's cellphones. We had to do something about it. Sometimes you have to shock people, and the message got through because I shocked them."

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His strong words came after a group of students were caught with naked images of a female student on their phones. The image was originally sent to the victim's boyfriend but following a breakup the image was shared with his friends.

Menzies said he spoke to female students about the consequences of sharing naked photos and talked to boys about "their disgusting behaviour".

"We had widespread issues of boys asking girls for naked photos and all that sort of carry-on."

He said he would not apologise for the comments he made.

"I don't give a toss, because you have to address issues at the time."

Some students were stood down from the incident but he could not say how many.

Detective Senior Sergeant Nigel Allan said police had investigated and resolved the incident. No charges were laid.

Menzies said students sending nude images was "as common as mud" in the schoolyard these days.

"This is what every teenage kid does. It is widespread right across New Zealand.

"The whole Roast Busters thing, that's the sharp end but below that it's so widespread. You go into any school in the country and that is the name of the game."

Awatapu College principal Gary Yeatman said the majority of students caught sending nude images were usually the younger ones as they hadn't thought through the consequences.

He said technology made accessing and passing images on a lot easier.

"Whenever possible, we look to educate students about the dangers of social media and the sharing of images.

"All students need to be mindful about what they post and ask for via social media."

Youthline national spokesman Stephen Bell said the organisation had been contacted six times since October about explicit images being shared.

He said it usually involved a jilted former partner who had decided to send the images as a form of revenge.

Ministry of Education head of sector enablement and support Katrina Casey said schools were not obliged to contact the ministry in relation to any incidents, but "we give them any support or help if they need it".

Schools are advised to contact NetSafe or the New Zealand School Trustees Association for further help or advice.

Youth One Stop Shop director Trissell Eriksen advised victims to talk to someone they trust, contact NetSafe and take screenshots of any messages or posts.

NetSafe operations manager Lee Chisholm said the sending of nude photographs had become quite normal in New Zealand's secondary schools.

The internet watchdog received about one complaint a week, Chisholm said.

"[Parents] should talk to their children before they think they are ready for it."

One such case involved a 9-year-old. Parents should speak to their children about sending and receiving explicit pictures, and reinforce that it was not OK.

"It's impossible to control it once it's been posted.

"What does that say about you? That person trusted you and you're betraying their trust."