Amy Gehring still faces four charges
The trial judge in the case against Amy Gehring directed the jury to clear her of the charge at the end of the prosecution case.
The 26-year-old science supply teacher was alleged to have seduced and had sex with the youngster, who cannot be named, at a New Year's Eve party.
Miss Gehring, a Canadian national who lives in Hampton, west London, still faces a further four counts of indecent assault.
'Encounters' denied
She is alleged to have had sex three times with another 15-year-old boy and once in an alleyway with his 14-year-old younger brother.
Miss Gehring was teaching at a school in Surrey when the alleged offences took place in November 2000.
Neither the school nor the pupils can be identified for legal reasons.
Giving evidence on Wednesday, Miss Gehring, who was brought up on her family's farm in a rural community in Otterville, Canada, vigorously denied any sexual improprieties or encounters with the boys.
Asked if she had ever had sex with the elder of the two boys, she replied: "No. Never."
She told the court that she had become friendly with one and that she found him attractive, but insisted she did not want a relationship with him, or with any other pupil at the school.
At the New Year's Eve party where she is alleged to have had sex with the same boy she said she was extremely drunk and being sick, and said she could not remember what had happened that evening.
Work placement
She testified that she believed all the children who had given evidence against her were lying, and insisted no sexual intercourse had taken place with any of the children.
Miss Gehring, who has a Bachelor of Science degree and a further teaching qualification, told the court that she had come to England alone on 28 August, 2000 having arranged work placements with a teaching agency.
She said she had come out of a five-and-a-half year relationship and come to teach in England because she "wanted to try to live my life without my ex-boyfriend in the background."
On arriving in the country, Miss Gehring said she had been lonely and had no friends or family to turn to.
'Glorified babysitter'
She told the court: "I kind of had a schedule, but I was thrown into classes.
"I never had breaks, I covered everything. Basically I was a glorified babysitter."
Asked by Mr Thompson whether she had experienced any inappropriate sexual conduct towards her from the children she replied: "Every day. There was grabbing, touching, gestures.
"It was out of control. I obviously didn't like it."
She went on: "I was disappointed. I wanted to go home but I didn't want everyone at home to think that I had failed."
The trial continues.