Teachers ought to know "considerable caution" is needed in Facebook communication with students, the Teachers Disciplinary Tribunal says.

A teacher has been censured after an "extremely foolish" Facebook exchange initiated by a 15-year-old.

Relief teacher Leon Paul Duffy told the Teachers Council Complaints Assessment Committee he had been "set up by a couple of girls thinking it would be funny".

But the Teachers Disciplinary Tribunal said Duffy should have known it was inappropriate to have personal Facebook contact with students.

"The behaviour was at the least extremely foolish, it could be regarded as having a sinister dimension, and it certainly demonstrates a failure to appreciate the nature of appropriate professional boundaries in a way that any reasonable member of the public would find significantly concerning," the tribunal said.

It found Duffy's behaviour was serious misconduct but was at the lower end of the scale, and said he may have acted naively.

The Facebook exchange took place last August when a year 10 student at an unidentified college where Duffy was teaching looked him up on Facebook and friended him.

During the exchange, Duffy told the student he was "super naughty" and asked her why she had made the friend request. When the student said she was in year 10, he replied: "I thought you were older. Ummmmm ...shall we stop messaging now so I don't get in trouble?"

Shortly after, he again asked why she had made the friend request, saying: "Be honest, promise I won't tell anyone as long as you don't?"

The student said: "...it was a joke so algoods aye".

"ha ha. Sweet as then. Hey.....don't tell anyone we are friends on here ok. Shhhhhhh," Duffy said.

The student agreed she wouldn't, and Duffy replied: "OK cool. I won't delete you then. Ha ha. Hey we can be bad ass and message each other in class next time I have you. He he"

The student said Duffy was twice her age, suggesting he was around 40.

Duffy queried how he could be 40. "I'm way too cute. Ha ha," he said. The student said she felt the conversation was weird, suggesting Duffy was risking his job, asking "don't you have a girlfriend?"

Duffy replied: "Why am I risking my job? You told me you wouldn't tell anyone so I'm trusting you. No girlfriend. You have a boyfriend? Ok maybe I can't trust you?"

The tribunal said there were also allegations about comments made in the classroom by Duffy, of "inappropriate hand signals" and of making comments about how a student looked in her PE gear.

The only evidence of those comments was a hearsay statement from the school's principal reporting allegations by a student. On the basis of the evidence, the tribunal said it could not make any finding on that point.

The principal had contacted police about the Facebook conversation. In an interview with police, which was videoed, Duffy said he had come to believe a group of students were telling each other to try to friend him to try to get access to his Facebook page.

Duffy had denied he had any "intentions", and police decided his actions did not meet the criminal threshold of grooming, the tribunal said.

Duffy told the Complaints Assessment Committee he had made a complaint to police about the student "because she got hold of my cell number and was prank calling me most of last month".

He also said he had received no income since his relieving work at the school finished, and he had no intention of going back into teaching and would be happy if his teaching registration was taken from him.

The tribunal said that without hearing from the student involved, it could not make any finding on Duffy's suggestion the initiation of the Facebook conversation may have been an attempt by the student, or more than one student, to draw him into an embarrassing exchange.

In any case, a teacher should know better, the tribunal said.

"Allowing oneself, as a teacher, to be drawn into this type of exchange, has the potential to quickly lead to a highly compromised situation."

While the tribunal found serious misconduct was established, it said the evidence did not establish whether Duffy's intentions were inappropriate. It censured Duffy but did not consider deregistration to be warranted.