A Pukekohe High School 15-year-old was held down and violated with a vehicle part after it was revealed he planned to move to a private boarding school.
The Herald understands the boy was assaulted behind the school gym after a group of boys surrounded him during a break, saying things like, "If you're going to [the school concerned] you deserve this sort of thing" and "This is what you will get in boarding school."
The victim, who was traumatised but did not require medical help, has not yet returned to school and the matter is now being investigated by police.
Pukekohe principal Ian McKinnon confirmed a serious incident occurred 13 days ago after a joke between a group of friends about the boy moving school "went too far".
"The incident involved a male student who was held by others and who was then assaulted.
"Whilst what took place may well have started out as a joke among a group who knew each other, its outcome was far from that. It was very upsetting for the victim and for a number of students in the area, many of them friends of the victim."
Mr McKinnon would not comment on whether a sexual violation had occurred, saying that was "the nature of the police investigation".
He did, however, classify what happened as "gross misconduct" and said the other students had been excluded - meaning they cannot return to Pukekohe College and must be enrolled somewhere else.
A Pukekohe student said the assault happened on the field behind the gym and started with two of the boys holding the victim down as a prank. "Another guy took it too far and pulled [the boy's] pants down."
Mr McKinnon said the assault was witnessed by a number of students, many of whom had since given statements to police, but none are believed to have had time to intervene as it happened quickly.
Detective Senior Sergeant Alan Symonds said interviews were being handled by the Counties Manukau child protection team.
Mr McKinnon said a letter was sent to parents outlining the school's response to what happened.
He told parents reactions to such an event would be "varied and can include intense feelings of shock, guilt, anger, anxiety or denial".
"As a school, we have a responsibility to provide support and assistance for those who need it and allay any concerns that may exist."
Mr McKinnon said he had been "stunned" by what had happened and the school had made it clear it would not tolerate such behaviour.
"Nobody condones this sort of behaviour or any type of physical assaults and it's hugely upsetting when people have to witness it, and they were upset about it.
"Kids just don't know when to stop with some of their behaviours."
In 2001, a Taradale High School student was held down and sexually violated with a broomstick at a party in Napier. Six students were later convicted of sexual violation and sentenced to 2 years in jail. A seventh was found guilty of indecent assault.
- additional reporting: Amelia Wade