O'Sullivan was already serving a jail term of eight and a half years for sexually assaulting 27 little boys when he pleaded guilty to assaulting another high school boy in the early 1970s.

The assaults on this child, which include what today's legislation regards as sexual intercourse but which in the 1970s was legally referred to as indecent assault, were not dissimilar to that experienced by many others, Newcastle District Court Judge Roy Ellis said on Wednesday.

"There's a bucketload of students over the years who this man victimised for a decade or more, and whose lives he ruined," Judge Ellis said.

In this case, the boy, then aged 13, was first abused during a technical drawing/industrial arts class, in a classroom full of children at Marist Brothers College in Hamilton.

The victim was brought forward to where the teacher, Mr O'Sullivan's desk was, and placed in a position where other students could only see him from the waist up.

"He had responsibility for the education, not the abuse of the victim," Judge Ellis said.

His pleas of guilty had merit, if only because it meant his victim did not need to put himself at risk of being re-traumatised by giving a victim impact statement, a police statement, coming to court to give evidence, being cross-examined, called a liar, and running the risk of the perpetrator getting off.

"A person can be remorseful, sorry you've done it, but not actually acknowledge what they've done," Judge Ellis said.

The fact that O'Sullivan still denied that he had homosexual tendencies, and that he couldn't come to grips with publicly acknowledging that was "just ludicrous", Judge Ellis said, and pleas of guilty did not necessarily mean he was remorseful.

O'Sullivan said he had no memory of the student, and given the number of his victims, that was plausible, Judge Ellis said.

O'Sullivan appeared via audio-visual link from prison dressed in long-sleeved prison greens, seated in a mobility aid, and occasionally taking notes.

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A victim impact statement was read out by the victim who said he has struggled throughout his life.

He hated school, and started stealing bottles of port, getting himself paralytic drunk every week, he said.

"By the time I was 17 I was doing it twice a week," he said.

At the age of 21, he was drinking to get drunk every day, until about the age of 38.

He was consistently fearful and anxious at school where O'Sullivan was "often lurking around".

"He would come from behind and hover over me at my desk," he said. " I could not do my work ... I felt unsafe at school and left before the end of fourth form."

He has never had a lasting relationship, and could not trust people who got close to him in case they discovered his past, he said.

He did not disclose O'Sullivan's crimes until the Child Abuse Royal Commission which was announced by then Prime Minister Julia Gillard in November, 2012.

"I hope to feel better for standing up for myself, and I hope it helps other men out there to have the courage to speak up for themselves," he said.

Judge Ellis sentenced O'Sullivan to another year in jail, bringing the time he will have spent in jail nine years by the time the 84-year-old is eligible for release on parole on August 28, 2025.

A total jail term of nine years for the destruction of 30 years was not a long time, Judge Ellis said, but nine years nonetheless was a lengthy period.

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