Strapping 6ft tall Will Cornick showed fellow pupils a 13in-long kitchen knife and boasted of his plot to attack petite Ann Maguire before he stabbed her eight times during her Spanish class.
He was also carrying a bottle of Jack Daniels whisky in his rucksack, along with the knife, which he pulled out and boasted: “It’s like a party.”
Cornick was 15 when he murdered Mrs Maguire, 61, at Corpus Christi Catholic College in Leeds in April, 2014.
He intended to go on to stab pregnant Sinead Miley in the stomach to kill the baby and then plunge his knife into the throat of year head Andrew Kellett.
Despite at least 10 students knowing Cornick was armed and had alcohol, none of them raised the alarm – either fearing Cornick would harm them or believing the threats he was making about killing the veteran Spanish teacher to be a joke.
Yesterday head of English Marie Coleman told the inquest into Mrs Maguire’s death how during the first lesson of the day she left the classroom for 10 minutes when Cornick began brandishing his weapon to classmates and revealing his murderous intentions.
She said why students failed to inform teachers was “unfathomable”.
One pupil told another teacher Emma Conway about seeing the knife but only after the stabbing.
Nick Armstrong, representing the Maguire family, asked Ms Conway why she thought none of the children reported it before Mrs Maguire was stabbed.
She replied: “I’ve no idea.
“I don’t know why any one of them wouldn’t have done.
“It beggars belief that they wouldn’t share that information.
Cornick was jailed for a minimum of 20 years at Leeds Crown Court in November, 2014, after pleading guilty to the murder of Mrs Maguire.
It was said that the pair had a “broken relationship” because the teacher had blocked his attempt to drop Spanish classes and banned him from a school outing.
The Maguire family have failed in High Court attempts to have children who witnessed the murder give evidence at the inquest in Wakefield.
Mrs Maguire’s widower, Don Maguire, 65, said “difficult questions” needed to be asked of the pupils who heard of Cornick’s disturbing plan.
The inquest continues.