Kandice Barber, 35, allegedly told the boy she could be pregnant with his child and threatened to ‘take him down with her’ if he told anyone about their affair.

Jurors heard how she had approached the child at a sports award evening, added him on Snapchat messenger and later asked him if he wanted to meet privately.

Barber allegedly picked him in her car and drove to a field to have sex and later sent the boy topless pictures of herself.

Prosecutors say the headmaster of Princes Risborough School, Buckinghamshire, found out what was happening after coming into possession of one of the pictures, which was circulating between pupils.

But the defendant, who denies a series of charges including breaching a position of trust, told police her Snapchat account must have been hacked.

Aylesbury Crown Court heard how after their first encounter, Barber, who has school-age children of her own, met up with the boy for two other illicit trysts.

Opening the case, Richard Milne, prosecuting, said: ‘It all started at a sports evening on September 27, 2018 when she came over to him and asked to borrow his phone.

‘She had possession of his phone, she put her details into his Snapchat account. He thought it was a bit weird as he was mates with her son, who was at the same school.

‘Things developed on her part by her sending him messages. She would tell him she was having a bath or a shower and then ask him if he wanted to meet.’

The court heard how after arriving in her car and asked if there was somewhere private they could go, the boy suggested some fields at 5pm on a school day, so they went there to have sex.

As photos of Barber began circulating around the school, so too did gossip that she had slept with the pupil, who cannot be named for legal reasons.

Mr Milne said: ‘He was not proud of what happened, he was not showing off, it was not some sort of fantasy. He was extremely concerned and nervous when the rumours were going around.’

Jurors heard how Barber had proposed staying at a hotel as a ‘special treat’ for the boy’s 16th birthday, which he ‘politely declined’.

By law teachers are not permitted to have sexual relations with students under the age of 18, even if they are over the legal age of consent (16), because they are in a position of trust.

In a video interview with police on March 11 last year, the boy claimed the two had continued messaging for months after he turned 16, only stopping because school staff found out.

When called in to speak to his headmaster, he says he initially denied having sex with Barber.

Speaking to a member of the child abuse team at Aylesbury police station, he said: ‘I lied because she had told me she could be pregnant with my child and I began to panic. I lied to pretty much everyone except my friends.

‘She said that if I was going to snitch, snake on her basically, she was going to bring me down with her.

‘I was like, are you going to accuse me of rape? She was like, dot dot dot. Obviously I got angry and I did not talk to her after that.’

Barber was arrested on March 12 last year and during her interview produced a prepared statement denying having sex with the boy.

She claimed her pregnancy was widely known around the school – although she later lost the baby – and that her husband was the father.

A social worker attended Barber’s home the following day for an assessment, at which point the teacher admitted to sending a naked picture but denied having sex with the pupil, the jury heard.

The court heard how she told the visitor that she started talking to the boy on Snapchat in September 2018 and that ‘he had befriended her first’.

She allegedly told the social worker she was ‘going through a bad patch with her husband’.

Having lost their child during her pregnancy, she said they wanted to try for another one but that ‘it was not happening’.

Mr Milne told the jury: ‘Things were strained between her and her husband. The boy had paid her attention and she had let her guard down and started to talk to him.’

The court heard how the social worker paid another visit, and Barber asked her not to include what she said in any official reports, warning she would deny having ever said it.

Mr Milne said: ‘The defence is likely to be that she, the defendant, did not engage in any sexual relationship with the complainant. In other words, it is simply made up.

‘Although it may well be accepted that she, in social media terms, accepted a friend request sent by the complainant to help him out with a problem that he was having with one of his friends, it was he who kept on calling her and pursuing her in what may be described as an unhealthy manner and threatened to tell a teacher that something was going on.’

Barber, 35, from Wendover, Buckinghamshire, denied three counts of causing or inciting a child aged under 16 years to engage in a sexual act, one count of sexual communication with a child, one count of causing or inciting a child to engage in sexual activities while in a position of trust and one count of causing a child to watch a sexual act by a person in a position of trust.