She said the school's handling of the situation had sent the wrong message to students.
"It's basically telling them that if a crime is committed against you at school, very little is going to get done about it."
The school principal said a restorative justice meeting was held between one of the students, her family, the boy and his caregivers; and the boy has been stood down.
A plan had been developed to help the girls feel safe for when the boy returned.
"We're not becoming a law enforcement agency. Students and their safety is our responsibility – we ensure their safety and take any further action that's required.
"Our response depends on the immediate risk. If a major incident is happening in school and we require police assistance, as any school would do, we'd call 111."
The "unusual incident" was reported by the school to police around three days later at a weekly meeting.
In that time the boy was immediately removed from the school while senior staff completed an investigation into the incident.
A Northland police spokesperson said it had a close relationship with schools in the region and provided regular support, advice, and direction through their school community officers.
"Typically schools have an internal process when dealing with most incidents involving students, and often police will not necessarily be notified or involved depending on the seriousness of the situation."
University of Auckland law expert Bill Hodge said incidents involving a weapon being used threateningly, without causing injury, warranted a police response regardless of the setting.
"There is no immunity for students to commit crimes on school grounds. An assault, aggravated assault, threatening to kill... are crimes wherever they are committed."
Hodge said incidents such as that at the school could be classed as common assault which carried a one-year offence.
The Ministry of Education's deputy secretary sector enablement and support Helen Hurst said it expected schools to call police when there was an imminent risk of harm.
She said schools were able to access ministry supplied practical guides, example policies and procedures, training in responding to behaviour, and the support of MoE regional staff "where needed".