Andrew Bolton claims he was unfairly dismissed from Church high school, Newcastle-upon-Tyne, after a disciplinary hearing sparked by rumours that he was having a relationship with sixth-former Shona Upton.
He insists his relationship with Miss Upton, now 19, began only after she had left the pound;2,233-a-term school, while she was awaiting her A-level results.
However, the school claims the affair started much earlier. One teacher reported her concerns to the headteacher after allegedly seeing Miss Upton grope Mr Bolton at a pub near the school.
Miss Upton, appearing before the tribunal on Wednesday, insisted they had simply been arm-wrestling to settle a good-natured disagreement about rugby.
The teenager, whose parents Philip and Maddy approve of her continuing relationship with Mr Bolton, told the panel that the rumours about a sexual relationship may have been started by "jealous" fellow pupils.
She said: "It's what girls do when there is an attractive young male around." She said she did not confront the gossip for fear of giving it credibility.
She also said that she would not have embarked on a relationship with a teacher while she was still at school."
The Newcastle university student said their relationship began at the beginning of August 2002, after a meeting in a pub. She also revealed that they had moved in together about one week after she started university in September.
Mr Bolton has told the tribunal he felt he had been picked on by head Lesley Smith and her deputy Yvonne Fleming. The former head of maths said he did not bring the gossip to the attention of Mrs Smith because he did not see what she could have done to curb it.
"If I was going to see the management about every rumour, I would have had to move into the head's office," he said. When it was suggested that he may have been unwise to offer extra help to girls in one-on-one sessions, he said female colleagues were not placed under scrutiny.
At an earlier hearing, a caretaker claimed to have caught the couple in a clinch while Miss Upton was still a student at the school. Genian Qeku said he saw the pair together on at least six other occasions and reported the incidents to the senior caretaker.
Simon Curry, the teacher's solicitor, suggested Mr Qeku was lying to "curry favour" so he could apply for the senior caretaker's job. Mr Qeku denied this.
Mr Bolton is claiming unfair dismissal and sexual discrimination against the school, which sacked him in December 2002.
Since launching his tribunal, he has been asked to resign from a teaching job in Northumberland.
The hearing was continuing as The TES went to press.