Sentencing Brian Smith to detention at Her Majesty's Pleasure, Mr Justice Kay told him: "What you did that day was a dreadful, wicked thing."
The teenager had battered Jade to death with a piece of window frame on the line near their homes in Bootle, Merseyside, because Smith was afraid that she would tell on him after he pushed her over and cut her head, Anthony Gee QC, for the Crown, told the court.
Denise Matthews, Jade's mother, said she could never forgive Smith."I would not want him to be free again because there's no room in society for people like him," she said.
Smith, who had behavioural problems and had attacked pupils at school, was 13 when he killed the nine-year-old in July last year.
He told police he had given Jade a lift on his bicycle but left her safe and well in a park, and persisted with denials of murdering the child until last month. He later confessed during a series of interviews with forensic adolescent psychiatrist Dr Susan Bailey, who was the Crown expert in the James Bulger case, and changed his plea to guilty yesterday.
Jade, a popular child from a close family and a schoolfriend of Smith's younger brother, suffered eight blows to the head from the piece of frame weighing more than 2lbs and another 20 blows to the arms and body as she attempted to defend herself.
The judge will now make a recommendation to the Home Secretary about the "tariff", or minimum, time that should be served for the purposes of punishment and deterrence, but he warned that Smith would not be released until it was decided it was safe to do so.
"At the moment, I make it clear, I think you are a very, very dangerous boy - not only because of what I know about this offence, but because of earlier events described in statements about you at school and your conduct while in custody."
Mr Gee said Smith told Dr Bailey that they had gone down to the railway line at Jade's suggestion. He was tired after cycling for some time and became angry when she kept insisting on being taken home.
"He pushed her. She fell backwards and hit her head on the ground. She was bleeding. He put her on his bike, intending to take her to his grandmother's for help."
It was when they reached the grandmother's that Jade said she was going to tell on him, Mr Gee said. "To avoid that, he took her away, riding as fast as he could back towards the railway line."
David Turner QC, for the defence, said that Smith was tearful each time he spoke of killing Jade. Mr Turner, who also defended Robert Thompson, one of the two killers of two-year-old James Bulger after abducting him from a Bootle shopping centre, said that Smith would be given intensive individual therapy.
"He accepts he did a terrible thing. But when he did so, it should always be remembered that he, too, was a child."
The judge rejected arguments that Smith should not be named because of the damaging effects of publicity on other family members, but said that photographs of Smith could not be used.
Bootle detectives said there were only superficial similarities with the Bulger case, and that Smith panicked and then killed Jade because he feared retribution from her protective stepfather.
Frank Dillon, the defence solicitor, said that Smith came from a normal family. "There is nothing about them that would set them apart from other members of the community," he said.
However, Smith was disruptive at school and had been expelled from St George of England School in Orrell after attacks on other pupils and lifting a girl's skirt.
He had recently begun attending a special school for children with behavioural difficulties.
Detective Superintendent Geoff MacDonald, who led the murder investigation, said that he did not believe Jade's initial injury was an attack.
Of the events at the railway track, Mr MacDonald said: "There is no logical motive other than a totally frenzied attack, which would indicate that he lost control.
"He might have panicked because she was injured and he was afraid he would get the blame. There is no evidence of any sexual attack."Reuse content