Peter Saunders, chief executive of the National Association for People Abused in Childhood, said Jeremy Forrest had been handed a "serious sentence".
Jeremy Forrest was due to be sentenced for child abduction today, having been found guilty of that yesterday, but before mitigation he was formally charged with five sexual offences. He pleaded guilty to all five.
In mitigation, his defence counsel said that he was disgusted with himself for lying and ashamed - that what he had done was against his principles.
But the judge said that his behaviour had been motivated by self interest and he chose to ignore the "cardinal rule" of teaching.
Solicitor Henrietta Ronson read a statement on behalf of Jeremy Forrest's family outside Lewes Crown Court after the today's sentencing.
She described the case as a "sorry episode for all concerned" and added that Forrest "is very sorry for his actions".
She also said they hoped that the "failure to properly act on early warnings" about the relationship would be investigated.
Forrest, wearing a grey suit, white shirt and tie, showed no emotion after he was sentenced but nodded to his family as he was taken down to the cells.
Judge Michael Lawson QC sentenced teacher Jeremy Forrest to four and a half years for the five offences of sexual activity with a child and one year for the offence of child abduction, to run consecutively.
He told Forrest:
Jeremy Forrest, who was jailed for five and a half years for abducting a 15-year-old girl and five counts of sexual activity with a child, has also been banned from working with children in the future.
Former teacher Jeremy Forrest has been sentenced to five and a half years in prison after being found guilty of abducting a 15-year-old schoolgirl.
He also pleaded guilty at Lewes Crown Court to five charges of sexual activity with a child.
Former teacher Jeremy Forrest has pleaded guilty at Lewes Crown Court to five charges of sexual activity with a child.
Teacher Jeremy Forrest has arrived at Lewes Crown Court. The 30-year-old will be sentenced today after he was found guilty of abducting a 15-year-old female pupil.
Teacher Jeremy Forrest who was found guilty of abducting a 15-year-old girl is due to be sentenced today.
A jury took less than two hours to convict Forrest yesterday following an eight-day trial at Lewes Crown Court.