Mrs Maguire was stabbed and died from her wounds in April
A 16-year-old boy has been given a life sentence after he admitted murdering Leeds teacher Ann Maguire.
Will Cornick stabbed Mrs Maguire, 61, in the neck and chased her from a room at Corpus Christi Catholic College, then sat down and said "good times".
The judge, ordering Cornick to serve a minimum of 20 years, said he had shown a "chilling lack of remorse".
Mrs Maguire's family said it was "looking to the future with a fragile hope".
The defendant stood flanked by two prison officers in the dock as the court clerk read out the charge.
He looked straight ahead and showed no emotion as he admitted murdering Mrs Maguire in April. The Spanish teacher suffered seven stab wounds to her back and neck.
The judge Mr Justice Coulson, at Leeds Crown Court, said it was "quite possible" that the boy would never be released.
Prosecutor Paul Greaney QC told the court the boy had "psychopathic tendencies" and had derived pleasure from the public nature of the killing, something the judge referred to as "truly grotesque".
Prosecutor Paul Greaney QC told the court pupils had noticed disturbing aspects to the boy's personality.
He told other children that he hated Mrs Maguire and wanted her dead, writing in a message on Facebook that she "deserves more than death, more than pain and more than anything that we can understand".
The prosecutor said: "Late on the night of Christmas Eve 2013, and into the early hours of Christmas Day, the defendant exchanged messages with a friend on Facebook.
"In those messages he spoke of 'brutally killing' Mrs Maguire and spending the rest of his life in jail so as not to have to worry about life or money."
The court heard that Mrs Maguire had been leaning over her desk helping a girl with her work when the boy attacked her from behind.
"The defendant approached his teacher and began to stab her in the neck and back," said Mr Greaney.
"Ann Maguire was 61 years of age, 5ft 2in height and of slim build.
"The defendant was a full foot taller and was armed with a large kitchen knife.
"To describe his attack as cowardly hardly does it justice."
The prosecutor said Mrs Maguire fled but was chased by the boy, who was "stabbing her as she sought to escape".
'Proud of what he did'
Mrs Maguire was stabbed seven times in her back and neck before colleague Susan Francis, alerted by children screaming, rushed her friend into a work room and held the door shut.
Mr Greaney said: "She was able to see the boy through a glass panel in the door. His face was emotionless and he then walked away."
The boy, who was 15 at the time, went back to the classroom and sat down "as if nothing had happened", the prosecutor told the court.
Floral tributes were left outside Corpus Christi School after the attack
"He said that he had stabbed Mrs Maguire," said Mr Greaney. "He added that it was a pity she was not dead.
"He said to the entire class 'good times' and spoke of an adrenaline rush."
The boy told a psychiatrist after the killing that he had a "sense of pride" in killing Mrs Maguire, the court heard.
Mr Greaney said that when the expert asked about the impact on Mrs Maguire's family, the boy replied: "I know the victim's family will be upset but I don't care.
"In my eyes, everything I've done is fine and dandy."
"It's kill or be killed. I did not have a choice. It was kill her or suicide."
But the prosecutor said the boy's actions were still "inexplicable".
"The parents are decent people and responsible parents," he said. "They are at a loss to understand how and why their son has turned out as he has and they have co-operated fully with the police and with the prosecution.
"It follows that this is not one of those cases in which a defendant's actions may find a degree of explanation in his family circumstances.
Mr Greaney added that the boy's academic reports "had generally been positive".
Sitting at the back of the dock, the teenager's parents listened intently to the details of their son's crime.
Don Maguire, the husband of murdered teacher Ann Maguire, described the attack as "evil"
Because of his young age, the judge and barristers did not wear their wigs and gowns during the hearing.
In a victim statement read to the court, Mrs Maguire's husband Don described the attack on his wife as a "monumental act of cowardice and evil".
Det Insp Paul Money, of West Yorkshire Police, said no person acting in authority could have foreseen the "cold-blooded" and "cowardly" murder.
He said: "I can't name the person responsible but he comes from a good home with decent, responsible parents."
Mrs Maguire had worked at the school for more than 40 years and had been due to retire.
Her sister Denise Courtenay said: "We will never recover from this pain and anguish.
"No amount of punishment can compensate us for what we have lost."