A 17-year-old Oamaru pupil who allegedly cut a fellow pupil with a knife on school grounds faces an assault charge.

Police were called to St Kevin's College about 10.25am after the pupil was involved in an altercation with a 16-year-old pupil, who received a small cut to the hand during the clash on Wednesday. He did not require medical treatment.

The older pupil was arrested and charged with assault and will appear in the Oamaru District Court on July 18.

It is alleged the 17-year-old took the weapon, a pocket knife, to school with him because he feared he would be attacked by the other pupil involved, police have said.

St Kevin's College principal Paul Olsen said the school would not comment on the incident while it was before the court.

Senior Constable Carl Pedersen, of Oamaru, said the school had "everything under control" by the time police arrived.

While he confirmed a knife was involved, the cut "could easily" have been caused by the handle of the weapon.

Investigations were continuing.

Snr Constable Pedersen said it was never a good idea to be armed with a weapon in a situation that could escalate.

"Taking a knife into any situation where there is going to be a confrontation is just escalating it. If you think you are at risk, you just walk away.

"It could have been worse, but in saying that ... it only takes one punch for someone to fall the wrong way and that can be a lot worse. I said to the young man, if you hadn't taken the knife, the boy might have punched you and he might have been the offender.

"I just think that if people are planning a confrontation like that, from either side, they need to take a step back and think of the stupidity and risk involved.

"While it might seem like it's going to be a little tussle, it might escalate."