Mrs Maguire, 61, was stabbed to death by 15-year-old Will Cornick at Corpus Christi Catholic College, in Leeds, in April 2104.
A jury at Wakefield Coroner's Court returned a conclusion of unlawful killing on Wednesday.
The jury added: "Overall communication leading up to the incident was inadequate.
"There were missed opportunities to share and record problem behaviour. "
It also said: "The safeguarding policy was not followed as no 'cause for concern' was recorded around the pupil's use of alcohol."