Will Cornick stabbed Mrs Maguire, 61, as she taught a class at Corpus Christi Catholic College, in Leeds, in April, when he was 15.
Leeds Crown Court heard how he showed fellow pupils some knives he'd brought with him on the morning of the murder.
The judge has said the teenager showed a "total and chilling lack of remorse" and may never be released for what he described as a "truly grotesque" act.
Speaking outside the court after sentencing, family friend Maurice O'Connell read a statement on behalf of Ann's husband and daughters, he said: "She will be remembered as life's partner, a mother, a sister, a nanna Ann, an aunty and a genuine teacher with a generous spirit who lead by example."
The sisters of Mrs Maguire said her spirituality was reflected in her "innate goodness and her joy of living life" and they pray "she will stay near us and guide us and comfort us for the rest of our lives."
Denise Courtney also revealed the pain her loss had caused the family, she said: "The tragedy continues as the lives of all those closest to Ann have been shattered. We shall never recover from this pain and anguish. No amount of punishment can ever compensate for the loss of Ann's life."
The sisters also thanked the Catholic Diocese of Leeds for helping the family through a 'traumatic' time.
Will Cornick has admitted murdering Ann Maguire
Also speaking after sentencing, Peter Mann, Head of CPS Yorkshire and Humberside's Complex Casework Unit, said: "This tragic case has shocked the nation. On Monday, 28 April 2014, a boy, then aged 15, repeatedly stabbed Ann Maguire, his Spanish teacher, in a classroom and fatally wounded her in front of her pupils.
"While his deep-seated hatred for Ann appears incomprehensible, we are clear that he calmly and methodically planned this cold-blooded attack on her. He attacked Ann while she was helping children with their work and completely unable to protect herself. He has continued to show no remorse whatsoever.
"The Crown Prosecution Service has worked closely with West Yorkshire Police to achieve this successful prosecution. He has pleaded guilty to Ann's murder and has been sentenced to life imprisonment with a minimum term of 20 years.
"His terrible actions have robbed Ann Maguire's family, friends, fellow teachers and pupils of a deeply-loved wife, mother and sister, a respected friend and colleague and an inspirational teacher.
"The thousands of touching tributes paid following Ann's tragic death have clearly demonstrated the respect and devotion in which she was held by all who knew her.
"Our thoughts remain with Ann's family."
Prosecutor Paul Greaney QC told the Court: "It is important that we should record that it is clear from the evidence that the parents of [the boy] are decent people and responsible parents. 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.
"On the contrary, [the boy's] family life was marked by love and support."
The prosecutor told the court that made the stabbing "all the more inexplicable".
But, he said, class mates had 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."
The teenager wore a grey suit and tie and looked straight ahead showing no emotion as he admitted murdering Mrs Maguire.
His parents sat at the back of the dock whilst Mrs Maguire's family sat in an area normally reserved for court officials.
Two months before the murder, the boy sent a message on Facebook which said of Mrs Maguire: "[She] deserves more than death, more than pain and more than anything that we can understand."
In a victim statement read to the court, Mr Maguire described the attack on his wife as a "monumental act of cowardice and evil".
Richard Wright QC, defending, told the judge 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.