A former school principal has been jailed for one year for repeatedly abusing an “incredibly vulnerable” student in his office more than 25 years ago.

Newman Junior College principal David Austin Christian sat the Year 7 child on his lap and indecently dealt with him twice in 1991.

The Marist Brother preyed on the 12-year-old after the child was bullied at a school dance and again after summoning the victim to his office.

Christian, who has been charged with four sets of child sex offences relating to incidents in 1982 and 1991, is currently serving a two-year jail term for indecently dealing with a child.

District Court Judge Mark Herron jailed Christian for an extra 12 months today, saying the former principal knew the child was particularly vulnerable when he abused him.

He said Christian, now aged 75, traumatised and confused the victim through his gross abuse of trust.

“Given your position of trust you should have been protecting the child and ensuring he was safe,” Judge Herron said.

“Your actions undermine the trust and confidence members of the public, particularly parents, have when they place their children in the care of schools.”

Christian was caring for elderly people in a Marist Brothers community in South Australia when he was arrested.

Defence lawyer Seamus Rafferty said his client had been a member of the Marist Brothers since about age 15 and did not have the opportunity to explore his sexuality.

He said Christian seemed to explore his sexual being through his “entirely inappropriate” behaviour with children.

“Clearly there is a very strong sense of remorse for having put these people through what they went through,” Mr Rafferty said.

“He is subject to a personal safety and wellbeing plan that is implemented by the Marist Brothers.”

Christian pleaded guilty to two counts of indecently dealing with a child under the age of 13.

Prosecutor Jehna Winter told the court Christian’s attacks on the Year 7 student were another example of long-standing behaviour and an ongoing sexual interest in children.