Emergency services responded to an incident at the Islamic College of Melboure on Wootten Road in Tarneit just before 3pm.
Police cars and ambulance were at the scene while parents were picking up children from the school, many parents had no idea what had happened.
One school boy sung out to his parents across the street “Someone was stabbed”.
Another child was heard saying it was someone in 6D.
A 12-year-old girl was treated for a non-life-threatening cut to her shoulder.
An 11-year-old girl is currently assisting the police with their enquiries.
Both parties are known to each other and the exact circumstances are being investigated.