Deputy Principal Ronan Bass says it was standard procedure to put the school in lockdown in such circumstances so 1800 kids were not running about while St John Ambulance helped the student.
Principal Kelvin Whiting told the Herald the accident happened in a main thoroughfare and the Year 10 student needed to be stretchered to the sick bay.
He said the student cut her lower leg but it's not yet clear how.
"It was serious enough that we had to stabilise her in terms of bleeding. Then we rang for the ambulance and put the school into lock down which means we could treat her. The staff and nurses did a great job."