Geelong Grammar was not safe for children at a time when the school's culture valued its reputation over the welfare of students, the child abuse royal commission has heard.
The prestigious school knew about an allegation of improper conduct by live-in boarding house assistant Philippe Trutmann in 1985 and failed to take any action, counsel assisting the royal commission David Lloyd said.
Trutmann went on to sexually abuse 41 boys including 14-year-old boarder BIW, who was expelled for speaking out.
The response to BIW's 1989 complaint was an appalling failure by the school and revealed "something troubling" about its culture, Mr Lloyd said in recommending possible findings by the royal commission.
"The failure to investigate or report the matter suggests a desire to avoid reputational damage to the school," Mr Lloyd said in a submission released on Wednesday.
"The fact that there was such a response from the most senior people at the school is consistent with a culture which valued the reputation of the school over the welfare of its students."
Had Trutmann been removed much earlier than in 1996, it was very likely at least some of his victims would not have been abused, Mr Lloyd said.
A number of students would likely not have been abused had long-time principal John Lewis investigated allegations of child sex abuse that came to his attention, Mr Lloyd said.
He said the 1980-1994 headmaster's handling of abuse allegations fell below the standards expected of a principal.
Mr Lloyd said by September 1991 at the latest, Mr Lewis had reason to believe the school had three current staff members who had been the subject of credible abuse allegations and still had access to vulnerable children.
"At that time, Geelong Grammar was an unsafe environment for children," he said.
Mr Lloyd said Mr Lewis did not treat the issue of child sexual abuse seriously and preferred the school's reputation to the interests and welfare of the students under his care.
He said Mr Lewis had an "utterly deficient" system in place where Geelong Grammar would not refer child sex abuse allegations to police unless the school was satisfied beyond reasonable doubt the allegations were true.
"The system did not protect and promote the interests of the students and it instead was a system that was designed to protect the reputation of the school in preference to the interests of students," Mr Lloyd said.
Mr Lewis, who became headmaster of England's elite Eton College after leaving Geelong Grammar, has told the commission the school's number one priority was students' welfare and wellbeing.
His lawyers rejected Mr Lloyd's submissions, saying Mr Lewis acted as best he could in difficult circumstances according to the knowledge and practices of the times.
Geelong Grammar has again apologised for the hurt and harm suffered by past students during "a dark period" in the school's history.
