Jenine Saville-King, 29, allegedly began the year-long relationship with the boy when he was 15.

She was “infatuated” with him, the court was told, and they met for sex in her home, hotels and even at his mother’s house.

When the boy tried to end it, she is said to have confronted him at a supermarket where he was

working and begged: “Tell me it’s all over to my face and I’ll leave you alone.”

Their meetings came to light only when his girlfriend discovered a photo of the pair on his computer and informed staff at the school.

But there was insufficient evidence against her and she was not arrested until the teenager confessed to his head months later.

Saville-King has pleaded not guilty to seven counts of sexual activity with a child and one charge of abuse of trust.

The teenager told St Albans Crown Court he had been attracted to the assistant year leader, who helped him and other students with their homework and coursework.

He began emailing her after getting the address from another pupil. They started texting each other and arranged to meet in her car outside a pub, shortly before the start of the summer holidays in 2004.

“I remember her saying she shouldn’t be doing this but we carried on driving,” he said. “I was nervous as well at first but I was glad to be with her.”

Although there was no physical contact on that occasion, they continued to meet regularly and were in a car park when they kissed for the first time.

Asked if it had been like “kissing your nan”, he replied: “No – snogging.”

Saville-King then allegedly began taking the boy to her house in St Albans, Hertfordshire, where they performed sex acts on each other “hundreds of times”.

He said he was never worried about her husband Paul, 37, coming home because he worked in London and was “always assured Jenine picked him up from St Albans station about 6pm”.

They had full sex for the first time after he turned 16 because the teenager “didn’t want her to feel bad about her having sex with him whilst he was underage”, the court was told.

Over the coming months, they met at her house, in hotels in Hertfordshire and a flat she owned in Dunstable. The even began skipping school on Fridays for sexual liaisons.

He said that as the relationship continued, Saville-King claimed she had left her husband or that they were no longer sleeping together.

She took sick leave for stress in February 2005 and had not returned when she started maternity leave in May.

That month she went on holiday with her husband but on her return “all caution had been thrown to the wind” and they had sex at the boy’s mother’s house on two occasions.

They were still involved in August 2005 when her baby was born – and allegedly slept together just three days before the birth.

They continued to see each other even after the boy’s girlfriend discovered the picture that same month.

She is said to have bombarded him with emails including one which said: “I dream of being far away from here with you and baby and starting again.”

By the end of the summer, however, the teenager told her he had a new girlfriend and wanted to end the relationship. It was shortly after that when Saville-King confronted him at the supermarket in Watford.

In November, the boy, who had left the school, was invited back to meet the head, and admitted to the affair.

Prosecutor Ann Evans told the court that Saville-King “became completely infatuated” with the boy, adding: “She had a sexual relationship with him and it wasn’t a passing fancy.”

When Saville-King was arrested in February last year, she allegedly told officers: “Yeah, I kind of knew this was coming” and then claimed the boy had made up the allegations.

“I consider that he has deliberately used the concern and support I have offered him and manipulated it into the false allegations I am now confronted with,” said the teacher, who now lives in Hook, Hampshire.