A teacher in his 60s touched a student's penis to check for abnormalities when he believed the teenager had passed out drunk in his home.
The man, who later said he was deeply ashamed of his actions, blamed his behaviour on Asperger's Syndrome, but said he was motivated by concern for the young man - who he believed might have had a genital malfunction because of his poor aim at the toilet.
The 66-year-old has now been censured for serious misconduct by the Education Council, formerly the Teachers' Council.
The 19-year-old was staying with the teacher as an international home-stay student.
In November 2013, the young man hosted a farewell dinner at a local restaurant prior to flying home the following week, and arrived back at the teacher's house "obviously intoxicated", according to the written decision of the council's disciplinary tribunal.
He fell asleep on a sofa. The teacher found him and after remarking, "Well, I think we should get you to bed", helped the student to his room. He then helped him remove his shirt and skinny jeans.
He believed the student had passed out on the bed, and proceeded to pull the student's underwear down and touch his penis for around a minute.
It caused the teen "a great deal of discomfort", and after the teacher left, and he could hear that he was asleep, the student phoned his mother for advice on what to do.
He was later collected by a friend, who took him back to her house, where they contacted police.
The teacher admitted touching the young man's penis, saying he had been concerned for his personal hygiene.
He conceded that his actions were "bizarre" and he was "deeply ashamed".
The man was charged with one count of common assault, after an initial charge of sexual assault was dropped.
The teacher's defence claimed he was trying to "test his assumption that the [student's] penis may have a malformation", and said his "bizarre venture without true insight" was a consequence of his Asperger's Syndrome.
He had "no intention to sexually offend".
The teacher pleaded guilty to the common assault charge, and was discharged without conviction.
The judge found that his behaviour was "completely out of character" and was an incident "completely at odds with decades of good service to others in the community, including a commitment above and beyond the call of duty to his role as a teacher at the school".
He had no previous criminal history.
The tribunal said it accepted the court's decision that the teacher was not sexually motivated.
It also accepted a neuropsychiatrist's assessment that the teacher had "a genuine desire ... to establish whether the victim had an abnormality or medical condition which might explain his inaccuracy when using a lavatory to urinate, [and] that a physical examination to establish that would, in [the teacher's] mind, have seemed like a logical and appropriate step to take, and that [he] was not motivated by any sexual interest in the victim".
The specialist said that as a result of the teacher's Asperger's disorder, he "would have been oblivious to any sense of impropriety", which the tribunal accepted.
It also accepted the neuropsychiatrist's conclusion that the risk of reoffending was "minimal" given the teacher's willingness to continue with ongoing therapy.
The tribunal also decided that the teacher's actions were "motivated by concern", albeit a "detached concern", and therefore did not warrant deregistration, and should not send an inappropriate signal to the public or the profession.
After "very careful consideration", it decided to censure him for serious misconduct, with a "series of conditions to ensure he gets the necessary level of on-going support" he needed, including a minimum of 12 months of therapy.
The council described it as an "unusual case", and said it was "not an easy case".