Police have questioned a 15-year-old boy and are looking for two more after they allegedly entered a classroom at Kerikeri High School during a lesson to attack a student.
The incident occurred in a Year 10 class about 1.10pm on Tuesday.
The victim, also aged 15, was badly bruised in what deputy principal Mike Clent called ''a nasty assault''.
The teacher, who tried to stop the attack, was not assaulted but she was shaken and upset. She was still at school and being supported by her colleagues, Clent said.
One of the alleged offenders was a student at Kerikeri High. He had since been suspended, the strongest action available to the school. The other two were former students.
The attack on a student during class time was unprecedented, Clent said.
''We've never experienced anything like it before.''
Kerikeri police Senior Sergeant Peter Robinson said one of the youths had been spoken to on Tuesday evening while the others were known but still being sought as of Thursday afternoon.
Robinson said he was concerned the assault took place in a classroom with students and teaching staff in the immediate area.
The alleged offenders were too young to face criminal charges so would be dealt with by the police Youth Aid section.
''We are working with the school on what reasonable steps can be taken to stop this sort of thing happening in future,'' Robinson said.
In an email sent to parents on Tuesday evening, Clent said the school was ''shocked and appalled'' by the incident.
''Despite the best efforts of the teacher, these young people entered the classroom and one of our students in that class was assaulted. The young people were quickly located and left the school grounds as the police were called. The police responded and are dealing with this situation,'' he wrote.
''We are also fully investigating what happened, and how, here at school and you can be assured that we will respond strongly to keep our students safe.''
The victim was cared for by staff until his family collected him. The school was staying in touch with them.
Clent said he had visited the Year 10 class that afternoon to reassure students the school would do everything it could to keep them safe, answer questions, and acknowledge how upsetting and frightening the incident may have been. He also outlined the help available if students continued to have concerns.
He said teachers were on duty around the school during break times but Tuesday's incident occurred before the end of a lesson.
Clent told the Advocate that staff had since increased their presence around the school grounds and would stay vigilant.
The school was calm and settled with students reassured by the extra adult presence, he said.
In late 2019-early 2020 the Advocate understands there were ongoing problems with former students, some of whom had been excluded from the school, congregating at the back of McDonald's and threatening other youths.
Robinson said those issues had ceased during the lockdown but he was concerned by the escalation of violence in Tuesday's incident.