Kandice Barber sent topless pictures to the victim, who cannot be named for legal reasons, via Snapchat, as well as a “live video” of herself masturbating.
During one incident, Barber had asked the victim to meet her at a private field where she then had sex with him.
Barber had attempted to manipulate the boy and had told him she would “bring him down with her” if the relationship was discovered. She also told the victim later that she was pregnant and was unsure whether the baby was his or her husband’s.
The 35-year-old, of Wendover, Buckinghamshire, had been working as a school cover supervisor when the crimes took place in 2018.
She was found guilty of causing or inciting a child to engage in sexual activity in January following a retrial and was sentenced to six years and two months in prison at Aylesbury Crown Court on Friday.
Barber was also handed a 16-month prison sentence for causing a child under 16 to watch sexual activity by a person in breach of trust and a further 10-month sentence for sexual communication, both to be served concurrently with her main sentence.
Handing down the sentence, recorder Bal Dhaliwal said: “You also sent images, including a topless image of yourself, and a live video in which you were masturbating. All of these acts are tantamount to you grooming him and pulling him in, and with significant planning on your part.”
The judge continued: “There is no doubt in my mind that you acted in gross breach of trust. You took advantage of a child in your care and groomed him for your own sexual gratification.”
Barber was “determined to silence” the victim, the judge said, and had told the boy to delete all messages and block her on Snapchat to stop evidence being found.
The judge added: “You already had authority over him by the nature of your position, and to use threats to bring him down so he would comply with your demands to remain quiet, which is what I find that you did, is in my view beyond despicable.”
Barber will be required to notify police of her personal details and address for the rest of her life, as well as being barred from working with children and vulnerable adults, and being subject to a lifelong sexual harm prevention order.
Summarising a statement from the victim, prosecutor David Povall said: “He feels that his GCSE results were not as good as they should have been, in part as a result of the impact of these incidents on him.
“As a result of his poorer-than-expected GCSE results he had to leave the good school he was attending and go to a sixth-form college where none of his friends were.
“In summary, he says that the defendant ... who was supposed to help students make the right decisions instead helped him to make all the wrong decisions.”
Following the sentencing, the NSPCC stressed the need for victims of child sexual abuse to be properly supported.
A spokesperson for the charity said: “As a teacher, Barber would have been well aware of the vulnerability of young people, and it was her duty to safeguard those in her care.
“But, instead, she exploited her position of trust to groom and abuse this teenage boy for her own sexual gratification.”
If you, or anyone you know, have been a victim of sexual assault, help is available. Visit the Rape, Abuse & Incest National Network (RAINN) website or contact RAINN’s National Helpline at 1-800-656-HOPE (4673).
Additional reporting by Press Association