Masterton Intermediate School, one of whose pupils was robbed at knifepoint.

A knife was held to a 12-year-old boy's throat as he was robbed on his way home from a Masterton school.

The Masterton Intermediate School pupil had his bike stolen in the incident on Tuesday afternoon.

Principal Russell Thompson said the boy was confronted by a group of about six or seven boys on High St, around the corner from the school.

"They gathered around him, and one 11-year-old took a knife, held it to his throat and asked him to hand his bike over," Thompson said.

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"He's a really good student. He's capable academically, very sporty ... he rang 111 and handled the situation very well."

Thompson said the group of boys had turned up to the school on bikes about 2.40 that afternoon.

Asked to leave by several staff members, they departed without causing any trouble. However, after they left, they intimidated several motorists by circling their cars on Intermediate St, before one went on to commit the robbery.

A family member later took the boy who pulled the knife to police. He has been referred to Youth Aid.

Thompson said staff had been shaken, and he wanted to see action taken.

"There are 50 to 60 bikes at school on an average day, and I want to know that these kids are safe biking to school," he said.

"It's easy to feel vulnerable when you're out there on duty. I'm angry that someone's done this to one of our kids, it's a real frustration ... I just want to know that something's going to be done."

Senior Sergeant Mike Sutton, of Masterton, said it had been upsetting for the victim.

"Certainly we treat it as a serious incident. We're concerned by the behaviour of the young person involved."

It's not the first time youths have caused problems at the school in the recent past. Last December, groups of kids as young as eight were thought to be behind a wave of vandalism that cost various Masterton schools thousands of dollars.