Over the course of several months Gary Vigar is alleged to have engaged in sexual activity with the child before he orally raped her.
The offending is said to have taken place in 2020 when he was aged 28 and employed at Oaks Park High School in Carshalton.
Vigar, now 32, from Purley, is on trial at Croydon Crown Court charged with rape, causing a person to engage in sexual activity without consent, four charges of inciting a child to engage in sexual activity and two sexual assaults of a child by touching – he denies all eight charges.
On Monday, prosecutor Szilvia Booker told the jury that the child was an “enthusiastic participant” at the start as she and Vigar began messaging online.
The child told the police: “He always made comments that me feel good. I liked that because nobody else had done that.”
Ms Booker said: “Those text communications, the prosecution suggests, moved on to FaceTime and WhatsApp and involved what we would suggest is sexting.”
The pair would phone late at night when his wife had gone to bed with Vigar asking her to say certain things as he masturbated, the court heard.
Police found over 2,000 messages between the pair, including a message from Vigar which said “I finish quick on FaceTime tonight you’re teasing me”.
Ms Booker alleged that their relationship soon became sexual in person, as Vigar “childishly” incited the girl to kiss him by betting her £6 that they wouldn’t do it.
Later he incited her to masturbate him and he digitally penetrated her with his fingers, the court heard.
Ms Booker said when Vigar told the girl he wanted to take her virginity she found that “oppressive”.
The child told officers: “I was scared that if I didn’t do something he asked… Don’t get me wrong, at the start I was taking part and was asking for it, but towards the end I didn’t really want it.
“He said he wanted to take my virginity, he always asked me to go to his house and I kept saying no.”
On one occasion Vigar is alleged to have orally raped the girl, pushing her head towards his penis despite her protestations that she didn’t want to do it.
Ms Booker told the jury that Vigar denies the allegations against him.
She said: “Not everything is in dispute. Mr Vigar, I’m sure if he comes to give evidence, will not dispute that there was a closeness between him and [the alleged victim].
“But he denies that ever developed into anything other than that, that it became a sexual relationship.”
Judge Elizabeth Smaller told the jury that allegations of sexual misconduct with children can cause strong emotions.
“Emotions are unlikely to help you try this case. Approach this with an open mind and try it on the evidence you are going to hear,” Judge Smaller instructed.
The trial continues.
