THE elite Knox Grammar has been accused of covering up 33 years of sex abuse which included students being plied with alcohol and cigarettes while teachers showed them sickening videos of paedophilia and bestiality.

One boy woke in his dormitory to find a man wearing a Knox track suit and a balaclava hiding under his bed and sexually assaulting him, the child sex abuse royal commission heard yesterday.

The man grabbed the doona, put it over his head and fled with the boys in pursuit.

It is alleged the man was a teacher, who was never disciplined and only resigned months later after being arrested while ­masturbating in his car outside the Wahroonga school, which bears the motto Virile Agitur — “do the manly thing”.

The “balaclava man” was alleged to be religious education teacher Christopher Fotis, who had told the schoolboy he “had a surprise in store for him that night”, counsel ­assisting the commission David Lloyd said.

Mr Fotis will be giving evidence, the commission was told.

None of the abuse was ever reported to the police by the school and one abuser was even given a glowing reference to get another job as a teacher.

The royal commission has begun a two-week hearing into how the school dealt with the abuse, which was publicly revealed in 2009 when a number of former students went to police.

Five teachers were criminally charged — Barrie Stewart, Adrian Nisbett, Craig Treloar, Roger James and Damien Vance — and another three were linked to sex abuse but the files have been lost or destroyed, said Mr Lloyd.

They include the files of a ­number of students who had made complaints of abuse.

“This hearing will examine how and why these and other critical documents have gone missing,” Mr Lloyd said.

NSW Ombudsman Bruce Barbour has admitted his office was wrong in not referring “serious” allegations of sexual abuse at Knox to police when a report was sent to him in 2004, the commission was told.

A former assistant headmaster, Dr Ian Rentoul, cried as he revealed that his own son, David Rentoul, had been abused while a student in the late 1970s by Barrie Stewart ­during piano lessons.

Dr Rentoul, who left the school in 1981, said the school had been “completely irresponsible”.

“I believe the school was more interested in protecting the reputation of Knox than ensuring the safety and welfare of its students.”

One former student referred to the school as a “paedophile ring”, while another will give evidence that most weekends he and other students were invited to join Stewart, Vance, Treloar and Nisbett in master’s rooms, given alcohol and cigarettes and shown pornographic videos of men having sex with children and animals, the commission was told.

Knox Grammar’s counsel, ­Geoffrey Watson SC, read a ­statement from the school “humbly and ­sincerely” apologising for its failure, but outside the commission former student Scott Ashton said it was a forced apology.

Mr Ashton, who will give ­evidence that he was abused while at the school from 1980 to 1985, said people’s lives had been ruined.

The hearing in Sydney continues.