Wigan-born Mrs Maguire, 61, was celebrating her 40th year teaching at Corpus Christi Catholic College in Leeds when she was stabbed during a Spanish lesson by Will Cornick, who was later jailed for life for murder with a minimum of 20 years.
Her killing, in front of a class full of students, is the only time a teacher has been murdered by a pupil in a UK school.
Cornick had threatened to kill Mrs Maguire in social media postings.
But in a report published on Tuesday, independent reviewer Nick Page, who was able to interview the teenager, concluded that: “No individual other than Will Cornick should in any way feel responsible for Ann’s murder.”
He said there were no warning signs known to staff or other agencies at the time, adding: “There are a number of suggested refinements to practice in Corpus Christi Catholic College but this is in no way to suggest that if implemented previously, they would have prevented Ann’s murder.
“What is clear to me, as the reviewer, is that no one could have predicted or pre-empted Will Cornick’s attack on Ann Maguire and following her murder, individuals and organisations acted courageously, coherently and professionally in supporting the school and affected people.”
The report outlined how Cornick had a happy childhood despite his “loving and supportive” parents splitting.
He initially did well at school but by December 2013 had fallen out with Mrs Maguire and told a friend on Facebook he wanted to kill her. He uttered several, similar statements over the following months.
The report said Cornick had decided to murder her four days before he did so.
The report said that, after a “normal” start to the day, Cornick made further statements about what he intended to do.
It said: “The police investigation highlighted that pupils had heard Will make such statements before and did not take them seriously. One pupil told police that Will had a dark sense of humour.”
During the Spanish lesson, Cornick picked up the larger of the two knives and stabbed Mrs Maguire in the upper back and neck seven times from behind.
The report said: “There were no credible ‘warning signs’ - behaviours or antecedent behaviours - that could or should have been picked up by agencies or professionals leading up to the murder.”
Mrs Maguire’s husband Don said the review “appears to be significantly different from an early draft report which we viewed some months ago”.
In a statement, he added: “Therefore our family shall need some time to read and consider its findings. Once we have completed this we will make a statement and I shall make myself available to answer questions.”