A biology teacher wept as he was disqualified from working with children after kissing a 17-year-old pupil.
Stuart Barley, 45, was earlier found guilty of engaging in sexual activity with a child while in a position of trust, at Ipswich Crown Court.
Barley who taught at a school in Ipswich, Suffolk, had a passionate kiss with the drunken girl after a school party in March 2007, the court heard.
He got a two-year supervision order and signed the sex offenders' register
Supported by guard
Judge Peter De Mille said the father-of two had been an exemplary teacher for 20 years and described the case as a tragedy.
"If this were not a deliberate grooming process it plainly had to some extent the same effect," the judge told Barley.
"It would appear that you showed a complete disregard to the proper boundaries between teacher and pupil."
The judge said he felt there was a "low risk" of Barley re-offending if he worked with children in the future.
Barley, who was supported by a court guard after breaking down in tears, had denied any wrongdoing but was found guilty by a majority verdict after a trial in March.