This means the Herald cannot report his specific role at the school.
The school's name has also been suppressed.
Detective Senior Sergeant Colin Higson confirmed the investigation, arrest and charge but could not be drawn on the specifics.
"Police are working with a school after allegations have been made against one of its employees," he said.
"Police are investigating a matter which involves a staff member and a student from the school.
"We take these matters extremely seriously and are working closely with the school to establish what has occurred."
Higson said the parents of students who "have had contact" with the staffer have been advised.
"Police are making inquiries to identify whether other students are affected."
The school principal said that in light of the suppression orders he was limited in what he could say about the matter.
"I do not wish to pre-empt or prejudice the police investigation or courts processes," he told the Herald.
"What I can say is that we are doing everything possible to support any students affected by this as they are our core focus.
"We are also mindful that this is an important time of year for assessments and examinations and so wish to minimise any distractions for students."
The principal said the school took action as soon as the allegations were made.
"I can confirm that we acted immediately that we became aware of an allegation and referred the matter to police and Oranga Tamariki [Ministry for Vulnerable Children].
"The staff member was immediately stood down and then suspended.
"The matter has been reported to the Education Council," he said.
The Herald has learned that a meeting was held late last week to inform relevant parents and staff about the situation.
