Mokoia Intermediate was put in lockdown after two girls "well known to the police" attempted to "stir up trouble" on the premises.
Principal Rawiri Wihapi said in a statement that the decision to put the school in lockdown yesterday was made at the end of lunchtime.
"Two local girls, not Mokoia students, and already well known to the police, decided to come on our grounds and attempted to stir up trouble."
He said the police were called and the girls were picked up by the police.
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Teachers headed to the field to usher children into the classrooms and a lockdown was in place for a short period, he said.
The teachers ran indoor activities for the afternoon until the school was certain the girls, who left the school, had been picked up, he said.
A police spokeswoman said police were called about 1.15pm to reports that people of concern were hanging around outside the school.
She said officers attended and spoke to those involved. No arrests were made.