Jeremy Forrest, 30, now faces a fresh police investigation after a judge questioned the evidence the girl gave during the trial and suggested he may have contacted her to get her to vary her account.
She claimed in court that she was feeling “suicidal” at the prospect of their relationship being exposed and he agreed to go with her to France to keep her safe.
But Judge Michael Lawson QC said her testimony was “very different” to the statement she gave to police after the pair were caught after seven days on the run last September and appeared “designed to support” Forrest’s “spurious defence”.
“She had clearly received assistance in relation to what she should say,” he said.
Judge Lawson asked prosecutor Richard Barton if there was evidence of collusion and was told there was “material to suggest indirect communication between an unknown third party”.
Police said they were aware of the matter and were investigating.
Forrest admitted five counts of sexual activity with a child when he appeared at Lewes Crown Court yesterday to be sentenced for child abduction.
The married maths teacher was not originally charged with sex offences for legal reasons linked to his extradition, which could not previously be reported.
The jury took less than two hours to convict Forrest of abduction on Thursday after an eight-day trial.
As the verdict was about to be announced, the defendant mouthed: “I love you,” to the girl, who sobbed and replied: “I’m sorry” as he was led back to the cells.
Forrest befriended the “vulnerable” teenager at Bishop Bell C of E School in Eastbourne, East Sussex, when she was just 14 after she turned to him for help with personal problems and developed a crush on him, his trial was told.
She had just turned 15 when they started having sex.
The court heard Forrest would pick her up in her school uniform and they would have sex in his car, in hotels and at his marital home.
He also sent the girl “indecent images” of himself showing his naked torso with his hands down his underpants. She responded with pictures of her breasts.
The police and the school’s failure to prevent Forrest running off with the girl has come under fire.
Teachers were first made aware of concerns about their relationship after a school trip to Los Angeles in February 2012. They were seen by several pupils to be holding hands on the flight home.
But Forrest failed to heed words of advice from colleagues and continued to pursue the girl.
And despite a further warning after inappropriate messages on Twitter were brought to the school’s attention, he was still able to continue seeing the girl.
Police were not alerted until September, when the girl’s home was visited by a police officer and a social worker and her mobile phone containing the indecent images was seized.
Fearing they were about to be discovered, Forrest, of Chislehurst Road, Petts Wood, Kent, booked them on a cross-Channel ferry from Dover to Calais the next day.
They were caught when a British bar owner in Bordeaux contacted police after recognising Forrest when he applied for work at the bar using a bogus name.
Sentencing him, Judge Lawson said he had subjected the girl’s family to “appalling distress” by taking her with him to France.
Pursuing a relationship with her “broke the cardinal rule of teaching” and it had been his duty to “stop her infatuation, not to fuel it”.
Judge Lawson said: “Your behaviour over this period had been motivated by self-interest and has hurt and damaged many people – her family, your family, staff and pupils at the school and respect for teachers everywhere.
“It has damaged you too, but that was something you were prepared to risk. You now have to pay that price.”