Stuart Kerner, a religious studies teacher, was found guilty of sexual activity with a child by a person in a position of trust in court.
However, the judge added that the married teacher had been led on by an 'intelligent and manipulative' girl.
'There is no evidence you groomed her,' Joanna Greenberg QC told him.
'If anything it was she that groomed you.'
The 16-year-old, who was described as troubled, lost her virginity to Kerner in a storeroom at Bexleyheath Academy, London which was locked via a keypad. This was allegedly because the teacher was left emotionally fragile following his wife's miscarriage, the very same week.
After the incident the girl told police: 'It felt special. But, I dunno, it wasn't really. And admitting that kind of hurts.'
The pair also had sex at Kerner's house which he shared with his wife.
Children's charity Barnado's slammed the judge's comments, with a spokesman saying: 'It is wrong to suggest that a vulnerable child is in any way responsible for their own abuse.'