Several Nelson College students have been stood down after "serious acts of bullying".
Organised fights are believed to have happened "half a dozen" times at the college's Fell House boarding hostel late at night during term 1.
Thirteen boys, including three boys in Year 13, were reported to be involved.
A source at the college told Fairfax that a group of junior students were encouraged to fight by two seniors after lights-out.
It is believed one of the senior students was a member of the school's first XV and has been sanctioned in relation to involvement in the school's rugby programme.