Emergency services were called to Carine Senior High School just after 10am (AWST) today.
Police said the girl stabbed a 16-year-old boy during the first period.
The boy was taken to Royal Perth Hospital with injuries not considered to be life-threatening.
The girl also received medical treatment in hospital.
Police said no other students were involved.
“There is no threat to the school or the wider community, the situation is contained,” WA Police said earlier.
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“The WA Police Force is working closely with the Department of Education to resolve some sensitive and complex issues involved with this incident.”
Carine Senior High School principal Damian Shuttleworth contacted parents in a letter.
“I want to reassure you that police attended, the situation was quickly contained and there is no cause for ongoing concern,” Shuttleworth said.
“We have prioritised support for staff and students following this incident.”
The girl is due to appear in Perth Children’s Court tomorrow.
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