A man has broken down at a royal commission hearing while giving a harrowing account of being sexually abused, assaulted, bullied, bound and choked at an exclusive Sydney boys school.

The witness, who is now in his 50s, told the Royal Commission into Institutional Responses to Child Sexual Abuse that he was abused in the first week he arrived at The King's School, in January 1972.

"I was sitting in the [recreation] room when one of the boys pushed me off a wooden bench seat that he was sitting on — it was his to sit on, not mine," he said.

"It ended in a few minutes when he took to my face and my body with his fists, he beat me until I cried then I ran off to the dorm."

The witness, who was 11 at the time, told the inquiry things got worse after that.

"A week later, or two, the same boy sexually abused me," the witness said.

"He was in the dorm naked reading a porn magazine and masturbating.

"I've never forgot how shocked I was — I'd never seen a man's erection before and I froze.

"He wouldn't let me leave until he finished and then he asked: 'Don't you like porn?'

"I was 11 years old, I didn't know porn existed until I arrived at King's."

The former student said for the next six years he was labelled "the poofter" at the school, and he did not report the abuse for fear of being beaten.

He said older boys ran initiations for younger students and he was forced to take part in a series of violent traditions including "black balling" — where boys would cover his scrotum with boot polish.

On one occasion he said he was set upon by five boys who held him down while he was sexually assaulted.

He told the inquiry he was often threatened with knives and deprived of liberty, on one occasion he was bound and choked with his school tie until he passed out.

He said the abuse took a heavy toll.

"My life at King's was so unhappy I became increasingly angry and depressed," he said.

The witness said teachers at the school turned a blind eye to the abuse.

"I was constantly and mentally assaulted by abusers, and other boys, right under the nose of masters and teachers — whose pastoral care medical teams were supposed to be in charge of my welfare," the witness said.

Teacher punished him, survivor says

The former student said that one teacher even sought to blame him for his predicament.

"He often remonstrated with me for failing to get along with other boys, my school work, my attitude," he said.

"He punished weak boys with neglect and made them be punished with pack drills — which were calisthenics [done] to the point of failure — and the boys would cry."

He said the situation became so dire that he considered suicide.

He told the hearing that he thought telling teachers was not an option, because of reprisals, and that he was too ashamed to tell his parents.

"How could I tell a soul that I'd been raped by a boy with his hand? And the whole school thought I was gay, and they beat me, and tormented me, and did unspeakable acts to me," he said.

The former student said King's had denied him access to his school records and had not apologised or made recompense.

He told the inquiry he suffered ongoing trauma as a result of his treatment, including depression and flash-backs.

He said he wanted the school to admit they failed him, and that it was "not the child … this kid didn't fail".

"I was made a victim for six years, and none of us that have suffered institutional abuse — be it sexual or otherwise — want to look like victims," he said.

"For [The King's School] to claim they didn't know anything like this was happening is totally incredulous."

School principal concerned about the school's image, says victim

Another man, John Williams, spoke at the hearing saying he was sexually abused at the King's School in Sydney in the 1960s, and he was rebuffed when he finally went to confront school authorities in 2002.

Mr Williams said he went to the meeting seeking acknowledgment of the abuse, rather than for compensation, but meeting with principal Tim Hawkes gave him little comfort.

"Tim Hawkes told me that he understood what had happened when I was at school however he was very concerned about the school's image, and said if it went public it would have a negative impact on the school," Mr Williams said.

"He also talked about the school not having enough money to help me."

The royal commission hearings continue.