Murdered school teacher Ann Maguire was stabbed to death by a pupil who later said he "couldn't give a shit" about the impact on her family, a court has heard.
The 16-year-old boy was sentenced to life with a minimum of 20 years, after pleading guilty to her murder.
He stabbed Mrs Maguire, 61, as she taught a class at Corpus Christi Catholic College, in Leeds, in April, when he was 15.
Will Cornick - who can be named for the first time after the court lifted an anonymity order - had no expression on his face when he committed the murder and even winked at a fellow student before he attacked Mrs Maguire. He also brought a bottle of whiskey to school to celebrate after the attack, the court heard.
He admitted murder when he appeared at Leeds Crown Court on Monday morning, watched by his "decent and responsible" parents, who were described by the prosecutor as being "at a loss to understand how and why their son has turned out as he has".
After his arrest, he told a psychiatrist: "I wasn't in shock, I was happy. I had a sense of pride. I still do.
"I know it's uncivilised but I know it's incredibly instinctual and human. Past generations of life, killing is a route of survival.
"It's kill or be killed. I did not have a choice. It was kill her or suicide."
He said that when the expert asked about the impact on Mrs Maguire's family, the boy replied "I couldn't give a shit," adding: "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."
Describing the killing, prosecutor Paul Greaney QC said: "Mrs Maguire was at her desk helping pupils. She was leaning over, looking at the work of a girl.
"The defendant approached his teacher and began to stab her in the neck and back. He attacked her from behind.
"Ann Maguire was 61 years of age, 5ft 2inches in 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 she was chased by the boy "stabbing her as she sought to escape".
Mr Greaney said Cornick had earlier told pupils he wanted to attack other teachers, including a pregnant woman "so as to kill her unborn child".
His school reports "had generally been positive", the court heard.
Mr Greaney said there was nothing to indicate to hiss parents or teachers a risk of "homicidal violence".
But, he said, pupils noticed disturbing aspects to his personality.
Cornick told other children that he hated Mrs Maguire and wanted her dead.
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."
Cornick, wearing a grey suit and tie, stood flanked by two prison officers in the dock as the clerk read out the charge.
He looked straight ahead and showed no emotion as he admitted murdering Mrs Maguire.
The teenager's parents sat at the back of the dock and listened intently to the details of their son's crime.
Mrs Maguire's family sat in the court, while the large public gallery was packed with members of the press.
Two months before the murder, the boy sent a message on Facebook about Mrs Maguire which said: "The one absolute fucking bitch that deserves more than death, more than pain and more than anything that we can understand."
He told a psychiatrist how he planned the murder.
The court heard Cornick had said: "I decided on Sunday it was going to be a knife. I thought I was just going to go to school and wait for her lesson and do it.
"I wanted to get caught. That's why I did it in school. I wanted to be in jail."
Richard Wright QC, defending, told the judge, Mr Justice Coulson, that this was "a sentencing exercise without parallel" and added: "In the UK at least - an offence without precedent."
He said the boy gave "no sign to anybody of what was to come". "Plainly, these were the actions of a deeply disturbed young man," he added.
In court, a victim impact statement from Mrs Maguire's widower Don said he felt he could "no longer be a dad" to his daughters, Kerry and Emma, after the murder of his wife.
He said: "I'm still a dad but cannot help my children understand, cannot help them come to terms, cannot help them lessen the pain. Mummy would have been so much better. I can no longer be a dad."
Mr Maguire described the dreams he had of living in a rural backwater with his "beautiful, vivacious, generous, caring" wife.
"Now all our dreams have gone forever," he said.
Daughter Kerry said the murder had robbed her of her mother, and her future children of a grandmother.
In her statement, she said: "Mummy was a constant. Her love was boundless and her heart was open. She was a beacon of light, guiding and protecting me through my life."
Mrs Maguire's other daughter Emma said: "Every morning, I wake up and I pray that this is all a bad dream, just a split second of hope which quickly vanishes and the horror of the reality sets in."
Her statement added: "She gave us so much love, I never felt alone in life, I had my mummy."
Mrs Maguire's sister Shelagh Connor told the court that her "baby sister" was an "essential part of me".
In her statement, Ms Connor said she felt she had failed to protect her sister.
She said: "For 61 years, I looked out for her. My life today seems to have lost meaning.
"My grief and sadness and anger overwhelm me when I think of all that Ann has been robbed of. She will never fulfil her great dreams and plans, she will not grow old with us, in the love of her family."
Another sister, Denise Courtney, said she was overcome with an overwhelming sense of loss.
Ms Courtney said the date of the murder will be etched in her memory forever.
She said: "The day when time stood still and my whole world fell apart."
Speaking outside the court after the sentencing, the sisters said: "The joy of living her life and the fulfilment of her hopes and dreams and passions have disappeared with this horrific, cruel, senseless and cowardly act.
"No amount of punishment can ever compensate for the loss of Ann's life. No amount of punishment can compensate her family for what we have lost in this beautiful, selfless, caring, patient sister, mother, wife, auntie and nana."
Mr Maguire, daughters Kerry and Emma, and nephews Daniel and Andrew added in a separate statement: "We look to the future with a fragile hope.
"We wish that nothing of Ann's life be lost, that she will be remembered as a life's partner, a mother, a sister, a Nana Ann, an auntie and genuine teacher with her generous spirit who led by example, always putting others first, especially young people."