An exclusive Auckland school will undergo a restorative justice process over two boys who had their throats cut during a school production of Sweeney Todd.

Photo: RNZ / Carla Penman

Two 16-year-old St Kentigern College students were hospitalised in April last year, with one suffering a serious wound, after performing in the stage musical about a barber who slits his clients' throats.

But the school will not be prosecuted.

The college said last year an actual cut-throat razor blade had been used as a prop, but that it was covered in duct tape and foam.

Now, a WorkSafe investigation has found the school board failed to ensure the health and safety of the students was not put at risk.

The school admitted full responsibility in a statement by its trust board to media and the community this evening.

Instead of prosecution, the school would take part in a WorkSafe process known as an enforceable undertaking.

As part of it, the school had to accept full responsibility, agree to meet with the victims and their families as part of the restorative justice process, pay reparation, and improve the wider health and safety of the school.

The deputy chairperson of the trust board said they felt "deep regret" over the incident.

"The trust board sincerely apologises for the fact that the accident happened and for the harm caused to all those families involved," the statement said.

"Saint Kentigern accepts that it should have done more to acknowledge the seriousness of what happened immediately after the accident."

If the school did not carry out all its obligations under the WorkSafe process, it could still be prosecuted for the original incident.