Music teacher Helen Goddard - nicknamed "the jazz lady" - befriended the youngster as they met for coffee after lessons.
Their relationship eventually became sexual, a development the youngster's parents scathingly condemned as a "complete betrayal" of trust.
London's Southwark Crown Court heard that the five-month affair included an overnight stay at her home and a romantic weekend in Paris.
Their forbidden trysts remained a secret until the school, which cannot be named for legal reasons, received an anonymous tip-off about what was happening.
Care workers were immediately contacted and police alerted.
When officers raided the teacher's housing estate maisonette in Thornham Street, Greenwich, south east London, they arrested the 26-year-old and seized various sex toys including vibrators and "fluffy handcuffs".
Goddard, a former child music prodigy, admitted six sample counts of sexual activity with the girl between February and July this year.
The disgraced teacher, wearing a white blouse and a black waistcoat and trousers bowed her head and repeatedly wiped tears from her eyes as Judge Anthony Pitts said: "This is a difficult case. The evidence showed you were having a full-on sexual relationship with the girl for many months.
"She has made it clear that the sexual contact between you was consensual and she says in her statement that in fact it was instigated by her.
"It is, of course, against the law to engage in sexual activity with a person under 16, even with her consent. These are serious offences in their own right. But the particularly aggravating feature evident here of course is that you were her music teacher throughout this period and from well before the sexual relationship started."
That meant a relationship such as theirs remained illegal until after the girl turned 18.
The judge said it was clear from the character references he had received that Goddard had been a "big hit" with her pupils.
One of her former colleagues, noticing girls "flocking to her room at break times", said she even warned her of the "dangers of being over-friendly and too popular".
"You are clearly an intelligent woman and a talented musician with a degree in music."
The judge continued: "Pupils are susceptible to abuse by those who teach them. The teacher's position of authority, their influence on the class, pupils' admiration of them, pupils' desires to be liked, their desire to impress or to be a special favourite makes it easy for a teacher, who so wishes, to take advantage of their pupils and start a relationship.
"In this case you clearly knew it was wrong to a start a sexual relationship with her and you knew the dangers to your career as a teacher.
"The relationship involved a fair degree of deception not only in respect of the school but also to the girl's parents. They made a statement they felt you betrayed their trust. They feel particularly betrayed by the deception of the Paris weekend.
"This case is so serious that an immediate prison sentence is inevitable."
The judge added she would also be banned from working with children for life and have to register as a sex offender for 10 years.
However, he had decided not to accede to a prosecution request for a sexual offences prevention order, which among other things would have banned her from seeing the youngster for an automatic five years.
The judge, who was told both the youngster and her former teacher genuinely loved each other, continued: "I have considered what has been said by the defence.
"I am conscious of the fact that whatever one thinks about what happened in this case, the girl appears to inevitably have suffered from what happened and this matter coming to light, and I have her interest in mind as well when I decided not to make this order.
"I think it would be draconian and unnecessarily cruel to her as well."
Goddard grew up in Farnborough, Hants, where she played the trumpet from an early age and was a member of Hampshire County Youth Band.
She was one of only five young musicians from England invited to play at the Sydney Olympics opening ceremony in 2000.
She not only raised the money for her air fare but practised for up to 13 hours a day in the weeks leading up to the event.
Regina Naughton, prosecuting, said the affair came to light on July 7 when the school reception received an anonymous email headed "concerned parent" and expressing concerns about a sexual relationship between a teacher and a pupil.
The following day it was followed by another, identifying the defendant and the girl and saying: "Please act quickly."
Once social services and the police had been informed, the girls' parents were contacted.
The barrister said when officers first spoke to the child she denied anything wrong had occurred, but 24 hours later confessed to her mother.
"She said she, the girl, had instigated the relationship and felt guilty for the situation she had put Ms Goddard in, and that she wished to continue the relationship.
"She also told her mother she was devastated that Ms Goddard would go to prison, and that she would not commit suicide as she wished to say goodbye to her."
In a later interview the youngster insisted that while "emotional and mature" for her age she poured out her problems to the defendant.
The support she received in return led to friendship and left her regarding her teacher as a sister.
"She describes the pair having feelings for one another, and that that was not planned or expected," said counsel.
"This developed into them flirting with each other and sending text messages to each other. They went for a walk one day and she describes kissing Ms Goddard on the lips, which Ms Goddard responded to."
The youngster also spoke of lying to her parents to stay at the trumpet teacher's home where they shared a bed and kissed.
Further lies and more overnight stays followed as the relationship developed.
Ms Naughton said the pair also had "sexual relations" at her parents' home.
In June, having declared they "loved each other" and told her parents she was going to spend a weekend with a relative in France, the girl and her teacher caught a plane to Paris.
"As part of the weekend, they went to the Gay Pride March," said Ms Naughton.
As the interview continued, the teenager told officers how her teacher spoke to her about leaving her job so their relationship would not have to stop.
She also spoke of the moment their affair came to light and how she urged the defendant to "lie and that they would get away with it".
Later she admitted "both of them knew what they were doing was legally wrong, but that it felt right". Since then the matter had "made her miserable and destroyed her".
Ms Naughton told the court that apart from the sex toys - which the defendant insisted had been used only on an ex-girlfriend - police also seized her mobile phone. The girl's was also studied.
They revealed 157 texts from the youngster to her teacher and 60 replies.
"Many of these were of an intimate and affectionate nature, some explicitly sexual."
One from the teacher read: "It's gonna be a beautiful day. I love you, you were on my mind all night."
The barrister also read an impact statement from the girl's parents.
In it they spoke of Goddard going "out of her way" to befriend them and their "vulnerable" daughter.
"However, under the guise of helping her we now understand that for over five months she was betraying our trust and our daughter's."
They continued: "She did not stay true to her professional responsibility."
The statement also spoke of the way they felt "particularly betrayed" by the Paris weekend, insisting: "We are deeply upset by the impact on our daughter by Ms Goddard's actions, which has serious and enduring consequences."
Explaining their daughter was now the subject of "intense teenage curiosity", they added they did not believe Goddard "fully understands the seriousness of breaking the boundary and completely breaching the trust of a teacher-pupil relationship".
But Anthony Heaton-Armstrong, defending, said his client was now "very remorseful" about what had happened and insisted she was "not in any sense a sexual predator".
