Three Nelson College students have been suspended or stood down from boarding over "serious acts of bullying".
A statement from headmaster Gary O'Shea and Board of Trustees chairman Dennis Christian said the school was dealing with serious disciplinary incidents which occurred in term one and involved 13 boys, three of whom were Year 13 students.
The senior administrators were only made aware of the issue last week.
The statement said the investigation resulted in one Year 13 student being removed from boarding and suspended from school pending a Board of Trustees hearing. Another Year 13 student was removed from boarding and sanctioned while one was stood down from boarding and sanctioned.
It was not clear what the sanctions involved.
"The incidents were serious acts of bullying perpetrated by a small number of senior boys and in no way represents the values and core culture of our school or our boarding institution," the statement said.
"We are devastated that a small group of boys have failed to assimilate any of this message which in turn has had a negative impact on some of our junior boarding students."
Fairfax reported the incidents involved groups of junior students being encouraged to fight after lights out by the senior students.
The school had been in correspondence with the parents of the students involved and support and guidance for the junior students had been put in place, the statement said.
"The college will now investigate the issue more broadly with the intention of understanding how these incidents came about and how to ensure that these similar matters cannot occur again."
The college was considering the most appropriate way to involve the police, it said.