Jobless loner given life for murder of too-trusting Claire.
Smith, who beat Claire, shot her with an air rifle and strangled her with her own tie as she made her way along a country road to school, was told he was a very dangerous young man who would go to prison for a "very long time".
Claire, aged 13, was murdered by Smith (20) after leaving her home in Eaton, outside Congleton, Cheshire.
A jury at Chester Crown Court took nearly six hours to unanimously find Smith, an unemployed fettler, of Clayton Avenue, Buglawton, near Congleton, Cheshire, guilty.
Smith dumped Claire's body in the fast flowing River Dane, where it was found five days after she disappeared on the one-mile walk to Dane Valley High School.
Judge Mr Justice Maurice Kay told Smith, who sat impassively in the dock with his chin on his hands on the rail: "You have been convicted on compelling evidence of a callous and brutal murder of a vulnerable young girl. Only you know precisely how she met her death.
"I am satisfied it was something which you planned in the same chilling way you contrived your defence in this trial.
"To anyone who saw you in the witness box it is apparent you have no sense of remorse for the terrible crime you committed and no thoughts for anybody but yourself."
The judge said Smith, who had been seen by eyewitnesses sitting in a field near to where the body was discovered on the morning of her murder, that psychiatric reports showed he had an emotionally unstable personality.
"I have no doubt that is correct. I have also no doubt it is correct, as the murder shows, that you are a very dangerous young man," said the judge.
At the time of her death the schoolgirl was in the process of being adopted by Robin and Kathryn Hart, from Eaton, who were in court to see her killer sentenced.
The judge said it should not go unremarked they had shown "remarkable fortitude and dignity" during their ordeal, which had been obvious to everybody. Smith had claimed he had seen Claire on the morning of her disappearance on June 18. But he said he had left her when she set off to walk to school and he had gone in the opposite direction.
But he was convicted after eyewitnesses told how they saw him with the girl and how water found on tracksuit bottoms in his bedroom matched that from the River Dane where her body was found. Mrs Hilary Archer, acting head teacher at Dane Valley High School, said in a statement: "The abduction and murder of Claire Hart whilst on her way to school almost a year ago has had a deep and lasting effect on many staff, pupils and parents at the school. For a child to set off for school, as on any other morning, along a safe and visible route and not to arrive is the worst nightmare."