Mother-of-two Clare Horton, 33, posted a series of self-portraits known as ‘selfies’, before her relationship with the pupil became sexual.
She showed him pictures of herself in a lacy top and a black dress with a plunging neckline while he was revising for his GCSEs.
The design teacher claimed she had been simply seeking ‘the hand of friendship’ from the teenager as she went through an acrimonious divorce and they did not have sex.
But she was found guilty of misconduct and banned from teaching for two years.
Mrs Horton, who was head of year 11 at the time, sent the teenager messages on Facebook while he was on study leave for his GCSE exams.
A disciplinary hearing was told she met the schoolboy for a revision time ‘rendezvous’ before driving him back to her home in Newport, South Wales.
The boy, known as Pupil A, later told police he had sex with the teacher but did not want to press charges because of his ‘strict religious beliefs’.
Mrs Horton worked at Fitzalan High School in Leckwith, Cardiff, for ten years.
A Professional Conduct Committee of the General Teaching Council of Wales heard that ‘a number’ of pupils had messaged her on Facebook.
She agreed to meet Pupil A and drove him to her home, where the pair are said to have had an afternoon sex session before she dropped him off at his home and went to pick up her two young children.
Rumours quickly spread in the school. After taking two weeks’ sick leave, Mrs Horton told head teacher Catherine Bradshaw that she had ‘slept’ with the boy and handed in her notice.
The head referred the matter to social services and the police but the Crown Prosecution Service decided to take no further action.
Mrs Bradshaw said Mrs Horton was well respected and her actions were ‘out of character’.
In a statement given to the disciplinary hearing in Cardiff, Mrs Horton said she had committed ‘the ultimate sin’, but denied that sex had taken place. She claimed that she simply chatted to the boy before falling asleep on the sofa for a couple of hours. ‘I was in an incredibly emotional state and sexual intercourse was the last thing on my mind,’ said the teacher. ‘All I took from Pupil A was the hand of friendship.
‘Because of what was going on at home, teaching was my only lifeline. To be told I was anything other than ugly, fat, useless and worthless was a safety blanket that I foolishly used.
‘He was very kind and listened. I was just talking about what was going on with my ex-husband. He made me feel better.
‘He slept at my house and so did I. I slept alongside him. We did not have sexual intercourse.’
The teacher, who broke down in tears while giving evidence, added: ‘Within days of the event, I felt I had committed the ultimate sin. I was in such a bad place mentally.
‘The feeling of shame and regret is something I will never be able to get rid of.’ She added that she ‘deserved to be punished’.
Martin Jones, who presented the evidence at the hearing, said Mrs Horton’s behaviour ‘clearly amounted to a significant breach in the professional boundary between her and pupil A’.
Panel chairman Helene Mansfield said the teacher’s arguments were ‘unconvincing’. She had displayed ‘a lack of awareness of her responsibilities and abused a position of trust’.
The panel chairman acknowledged that the teenager had been a former pupil at the time of the incident, ‘albeit by a few days’.
The disciplinary hearing ruled that Mrs Horton had engaged in an inappropriate and sexual relationship with the pupil that amounted to misconduct.
She was given an indefinite prohibition order and told she would have to wait two years before reapplying to teach.