A former St Edmund's College teacher Garry Leslie Marsh, 72, has been found guilty of molesting a student in the early 1980s.
Marsh was found guilty of 11 charges in the ACT Supreme Court over a series of incidents.
He put his head in his hands after the guilty verdicts were read out.
One of the jurors was overcome, leaving the court in tears.
Marsh was accused of grooming a vulnerable student whose parents had split up, even befriending the family.
He was charged with indecent assault for several incidents, including a serious assault when the boy was sleeping over at his house before a football match the next day.
Police not called until 2014
The boy, who was 13 at the time, told his mother what happened and a complaint was made to the school.
Marsh told the court the principal had to explain some of what he was accused of, because he said he had "never heard of it before".
He said he was then escorted from the building, after being told it was "in everyone's best interest".
Police were not called until 2014, when the victim decided to lodge a complaint.
The court heard that was prompted in part by the royal commission into child sexual abuse and the fact the alleged victim's son had turned 13, the age at which he had been assaulted.
Marsh has been released on bail to make arrangements for his elderly mother's care.
He will be sentenced in December.
