The 61-year-old was taken by surprise and stabbed seven times from behind with a seven-inch knife by Will Cornick, who held a grudge against his Spanish teacher at Corpus Christi Catholic College in Leeds.
As children ran screaming Mrs Maguire, bleeding heavily, ran to an office followed by Cornick, who moments later as his victim lay dying, smiled at a police officer who arrested him, Wakefield Coroner's Court heard.
A paramedic said the victim suffered the worst stabbing injuries he had ever seen, including one wound that had gone completely through her body from back to front.
Coroner Kevin McLoughlin began reading a series of witness statements, including that of Susan Francis, head of modern languages at the school.
Ms Francis said in her statement she was in a staff office when she suddenly heard "all this screaming" and youngsters "running down the corridor, screaming looking horrified".
Mrs Maguire then appeared holding the back of her neck, saying: "He's stabbed me in the neck."
Ms Francis statement continued: "She came running into the office, then the lad followed her. Then I shut the office door and put my foot against it. It was literally a split second.
"He just stood looking at me. No emotion. I just remember his face having no emotion. Like a mask on his face.
"I could see cuts on her jumper and lots of bleeding coming out of her neck.
"She said, 'I can't breathe. I'm dying.' I just kept stroking her and kissing her. She knew she was dying.
"Her colour was going. The ambulance people arrived, their faces looked like they had walked into some kind of Armageddon."
Paramedic Carl Sagar was first on the scene and rushed Mrs Maguire to hospital.
He said in his statement: "Ann was conscious throughout this. On the way down in the lift Ann stopped breathing. We commenced CPR.
"In all my career the stab wounds inflicted on Ann were the worst I have ever seen."
As the victim was taken to hospital Pc Katie Myles was called to the school where she had a bizarre exchange with Cornick as she arrested him.
He first asked her for ice for his hand which he had hurt.
Her statement continued: "Cornick then asked me, 'What is your favourite movie?'
"Cornick then asked, 'What is your favourite adrenaline sport? I love adrenaline sport. Cornick then smiled showing no remorse for what he had done."
No defence injuries
Meanwhile a trauma team had been prepared for the arrival at Leeds General Infirmary of Mrs Maguire where an emergency operation was attempted.
Medics carried out resuscitation attempts for 40 minutes before, in the presence of her husband, a decision was made to stop, at 1.10pm.
A pathologist report found there were no defence injuries and she had been stabbed seven times in the back after being "taken by surprise" with the fatal wound being 'stab wound three' to her jugular.
Cornick had told at least 10 other children what he was going to do to Mrs Maguire but they did not tell staff.
The dedicated teacher, described as the "mother" of her school, had clashed with "intelligent" but "weird" Cornick after she refused to let him drop Spanish studies, the inquest heard.
He was jailed for life for murder and ordered to spend at least 20 years in custody.
The inquest was adjourned until tomorrow morning.