A science teacher who slapped a 14-year-old pupil's bottom in class and called her a "naughty girl’’ was found guilty today of unacceptable professional conduct.

Trevor Towers was teaching a Year 10 class at Trevethin Community School in Pontypool when the incident happened in 2004.

The girl was so upset by the incident that before it went to court in 2005, she attempted suicide, a professional conduct committee of the General Teaching Council for Wales was told.

The panel heard evidence that the teenager, identified only as Pupil A, was bending over a printer when Mr Towers slapped her.

Returning the guilty verdict, panel chairwoman Jacquie Turnbull said the teacher's behaviour fell "far short of the standard expected’’ before retiring to consider what sanction to make against him.

Mr Towers was charged with indecent assault and sexual assault. He was bound over to keep the peace after no evidence was offered at a trial at Cardiff Crown Court.

He did not attend today's Professional Conduct Committee hearing.

The girl sobbed as the Cardiff hearing was told details of the July 2004 incident.

In a statement made to police read out at the hearing, she said: "The paper in the printer had jammed and I leaned over to try to fix it.

"I then felt a firm slap to my bottom and heard Mr Towers say 'You naughty girl' to me.

"I didn't know where to turn. I felt incredibly embarrassed that he had done this to me in front of my classmates.

"I felt myself turn bright red.

"I felt really upset and just wanted to get out of the classroom. I couldn't believe what had just happened.’’ Her friend, referred to as Pupil B, told police: "I saw him smack Pupil A on the bottom, but he left his hands on her bottom for a couple of seconds.’’ Mr Towers apologised to the teenager when the lesson finished, but told her he did not know why she was upset. He dismissed the incident as end-of-term "banter’’, the panel was told, but eventually admitted slapping the girl.

In her statement, the girl said: "I felt it was not right Mr Towers should treat me like that.

"I couldn't understand what I had done to make him pick on me.’’ The girl tearfully told her mother what had happened when she returned home and the pair went to the school together the following day, when Mr Towers again apologised.

The girl then reported the matter to police in Cwmbran.

She added: "I found this whole episode very distressing. I didn't make my complaint to the police lightly.’’ Her mother told the hearing today her daughter tried taking an overdose before the matter went to court in 2005.

She said: "She has had a lot of problems since all this happened. She even tried to take an overdose.

"When the police took it to court in Cardiff it was just too much for her. She has been terrible over it all.’’ Mr Towers, a teacher of 22 years' experience, was dismissed from the school, which has since closed, in January 2006.

Headmaster Royston Toon told the dismissal hearing at the time: "I found it amazing that an experienced teacher would not understand why slapping a girl would upset her.

"Would I have any trust regarding him being left with children? The answer is no.’’ Mr Towers told that hearing: "I said I was really sorry. I couldn't understand why she was so upset.’’ He described the slap as a "silly thing to do’’, and said he had no sexual or violent intent.

Mr Towers was allowed to continue teaching, but was given a conditional registration order. Ms Turnbull said he was to complete a training course "to update his knowledge and understanding of safeguarding children in schools’’ by July 31, 2009.

She said the panel took into account the fact it was a "single event in a career of 22 years’’ but added there were "areas of practice in need of retraining’’.

The hearing was told the Secretary of State for Education had earlier decided not to bar Mr Towers employment as a teacher.

He was given 28 days to appeal the decision.