Concerns raised by children about the growing closeness between married maths teacher Jeremy Forrest, originally from Inverurie, Aberdeenshire, and his pupil were "repeatedly dismissed".
Instead, Bishop Bell Church Of England School in Eastbourne, East Sussex, adopted a "default position" of "intuitively supporting a colleague" in the face of evidence that he might be an abuser.
It was also revealed the girl, who cannot be named, was never spoken to by school staff in a supportive way, according to the serious case review by the East Sussex Local Safeguarding Children Board.
The school's failure to involve the girl's mother in responding to events was another "cause for concern" and she was "denied the opportunity to assist her daughter", the report said.
Forrest, 31, was jailed in June for five-and-a-half years for child abduction and five charges of sexual activity with a child.
The case of Forrest and the girl, referred to in the report as Child G, attracted worldwide attention after he abducted her to France and they spent seven days on the run. Even after they came back and he was arrested they continued in a relationship. It was only in recent months that the girl declared the relationship was over.
The report reserves particular criticism for the school, with some staff failing to recognise the child protection implications in some events and believing Forrest was the victim.
Evidence of an inappropriate relationship between him and the girl first surfaced during a school trip to America in February 2012.
Two pupils approached the head of the upper school and reported rumours that the girl had a "crush" on Forrest since the trip.
Forrest denied any inappropriate relationship to senior staff and no other agency was involved, the report said.
Some information was given to the girl's mother, who was said to be satisfied with the way the school dealt with it.
The report said: "It is striking that it was, overwhelmingly, young people who raised concerns about this situation. Those concerns were repeatedly dismissed. Serious case reviews have often commented on agencies' failures to hear the 'voice of the child' but this has generally been a reference to the abused child.
"Here the very nature of the abuse, grooming and exploitation, made it unlikely that the victim would raise concerns. Yet agencies, and particularly the school, were too ready to dismiss the reports received from other children."
The report also highlighted serious concerns about the way information was recorded, stored, retrieved and provided to the authors by the school.
A raft of recommendations were made for professionals, including the school, East Sussex Children's Services and Sussex Police.
Terry Boatwright, executive head teacher atthe school, apologised for the failings and said they had been working hard to address the issues. He admitted the school "did not act with the correct level of investigative rigour, administrative efficiency and consideration for the concerns" raised by pupils.