Concerns raised by pupils about the growing closeness of teacher Jeremy Forrest and a teenage schoolgirl were 'repeatly dismissed', the report found.
Instead, Bishop Bell School in Eastbourne adopted a position of "intuitively supporting a colleague" in the face of evidence he might be an abuser.
Forrest, who's 31, was jailed in June after being found guilty of sexual activity with a child and for abducting the girl and taking her to France
The report also revealed that the girl, who cannot be named, was never spoken to by school staff in a supportive way.
And 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.
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Mostly dry with sunny spells throughout the day. Some isolated thundery showers are possible in Kent this morning and feeling fresher
Sunny this evening, then dry overnight. There is the risk of thundery showers for Kent tomorrow morning, then sunny spells by the afternoon
Sunshine to end the day then dry tonight. Tomorrow will be mostly dry and feeling fresher with the risk of a heavy shower in the afternoon