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Police responded to the incident, which took place outside Coupland's Bakery.
It is believed up to six pupils, all in uniform, congregated outside the bakery and one girl allegedly attacked another member of the group.
Several adults witnessed the incident and attempted to intervene, before police were called.
Waitaki Girls' High School principal Tracy Walker said police had contacted her in relation to the incident.
She confirmed the school had launched an investigation, which was ongoing.
The pupil arrested and charged had been suspended and will face the school's board of trustees, which will address her future, and two pupils have been referred to Youth Aid.
''The school is dealing with the issue. Obviously, some of our students are involved and affected by it,'' Mrs Walker said.
''Obviously, this kind of incident does not happen very often ... it was a shock and we are dealing with it.''
The school did not tolerate any form of violence or bullying and programmes were in place to educate pupils about what was expected of them.
''These students' behaviour crossed the line,'' she said.
The school was working with all pupils and families affected by the incident.
Mrs Walker did not believe Monday's incident pointed to bullying or violence issues at the school.
The pupil arrested will appear in the Oamaru Youth Court on March 21.