A former Newcastle and Sydney school teacher has spent his first night in jail after being found guilty of 21 child sexual abuse offences.

Edward Smith Hall, 68, known as Ted Hall, pleaded not guilty to 31 sexual and indecent assault offences between 1973 and 1986.

He was found guilty of all but 10 of the offences.

The 11 complainants were students at St Pius X High School in the Newcastle suburb of Adamstown where Mr Hall was a maths, history and geography teacher.

The boys were abused at school, in Mr Hall's unit, in the surf and on trips away.

Mr Hall, an ex-army sergeant, went on to teach at Newington College and Trinity Grammar in Sydney.

Key points: This victims were students at St Pius X High School in Newcastle

This victims were students at St Pius X High School in Newcastle A fire at the school in 2012 destroyed evidence

A fire at the school in 2012 destroyed evidence Hall will be sentenced on December 13

The judge-only trial was presided over by Newcastle District Court Judge Tim Gartelmann.

Yesterday he delivered a marathon judgement lasting six hours.

He found not guilty charges in relation to three boys, saying evidence available to him could not support the charges.

He noted a school fire in 2012 had destroyed evidence and that had put Hall at a disadvantage.

Fire ripped through Adamstown's St Pius X High School in 2016, destroying archival records and photographs. ( Supplied: YouTube )

One boy, known to the court as PM, said he was abused several times on trips away, as well as in Mr Hall's Merewether unit.

The boy said he was at the unit to help Hall move his belongings to another apartment.

"He had baby oil and asked me if I wanted a grease and oil change," PM said.

Judge Gartelmann said that "the words struck me as being consistent with what one might expect to be such an escalation of the conduct between them".

"He told his mother he never wanted to return to him again.

"When giving her evidence, I vividly recalled her shock and I felt PM's evidence was wholly convincing."

Threat to kill boy's parents

The judge also spoke about the truthfulness of another boy, DK.

DK told the court he originally admired Hall as he had befriended him and encouraged him in his rugby pursuits.

But DK said that all changed when Hall raped him in 1984.

"I was lying on my stomach, I felt smothered, I couldn't move," he said.

When DK managed to break free, the court heard Hall told him not to talk or he would tell everyone he was a "poofter". He also threatened to kill his parents.

DK ran away and went to a toilet to clean himself up.

The court heard he ran into Hall a decade later and had broken down while telling his flatmate about what had happened.

Hall then ran into DK again at his workplace. A colleague told the court about DK being frantic and distressed, before telling her Hall had abused him.

"This was all utterly convincing evidence," Judge Gartelmann said.

Boy was told teacher was dead

The court heard Hall told another boy, RD, that he was a practising nudist when he took the juvenile on a trip to the Barrington Tops.

"He said he was a practising nudist and said, 'I am getting my gear off, do you want to get your gear off too'?" RD told the court.

Hall then put sunscreen lotion on the boy and asked the boy to put it on him.

RD then asked to be driven home.

Several years later RD told his wife about Hall, and in 2004 went to the Catholic Education office to complain, only to be told that Hall was dead.

He said when he saw Hall in the media after being charged in 2016 he was shocked.

"I saw a news article and contacted police that day," he said.

"When I saw him you could have blown me over with a feather," he said.

Other boys complained of crushing handshakes and being taunted by being called "poofters" or "dogs".

St Pius X High School in Adamstown where Edward Smith Hall, known as Ted Hall, was a teacher of maths, history and geography. ( ABC TV )

Mother said police did not act when she reported abuse

Hall's second last victim, DG, was assaulted in 1985 and 1986.

The court heard he shared the common interest of rugby league with Hall.

Once the abuse started, DG told the court Hall would assure him that "it is not gay, it is normal".

But DG said he was confused after Hall later approached him and apologised, blaming alcohol and medication for his actions.

Hall denied he ever apologised or ever abused him.

The judge disagreed.

The court also heard the boy's mother complained to police in 1986, but they did nothing.

"We went to Hamilton to see detectives and gave a statement that took most of the morning, but police got a call for urgent assistance and they said they'd be in touch, but we did not hear back from them," DG's mother told the ABC.

"The police did not seem very interested.

"The police made hand-written notes but nothing was signed, the police terminated the interview and we did not hear from them again, there was no investigation."

Survivors unite after verdicts

The Newcastle District Court gallery was packed for the judgement.

As each count was dealt with they held hands, took deep breaths and watched intently.

As the series of guilty verdicts were read out, there was an audible gasp.

When Judge Gartelmann gave the tally of 21 guilty verdicts, there was spontaneous applause.

Hall's bail was revoked and, as the sheriffs took him by the arms, people yelled out.

"Bye, bye, Teddy. Off you go. See you Teddy. Bye, bye rock spider"

Hall zipped up his travel bag, put his glasses into a case and showed no emotion as he was led away.

He will be sentenced on December 13.