Liberty Baker died after being struck by Robert Blackwell's car as she walked to school in Witney, Oxfordshire
Two of her friends, also 14, and a man were also hit in Curbridge Road and needed hospital treatment.
Blackwell, 19, of Hayway Lane, Bampton, admitted causing death by dangerous driving.
He also admitted causing serious injury by dangerous driving, on 30 June last year.
Blackwell was disqualified from driving for five years at Oxford Crown Court.
A witness statement from Liberty's father Paul, read in court, said: "Since Liberty's death, our lives have been severely shattered and we feel utterly devastated.
"The future milestones that we would have taken for granted, such as Liberty wearing her prom dress, going to university, her 18th and 21st birthdays and being able to walk her down the aisle on her wedding day, have been cruelly taken away from us."
Prosecutor Ian Hope said Blackwell was travelling at "a minimum of 44mph" in a 30mph zone when his Citroen C2 struck Liberty.
The defendant admitted to police he had smoked cannabis the day before the crash after levels of the chemical THC were detected in his blood.
Mr Hope said Blackwell was "distracted for what must have been a period of time of 10 seconds or more".
Blackwell's vehicle also struck Paul Cracknell, who was walking on the pavement behind the girls. He is still being treated for the serious leg injuries he sustained.
PC Sandra Terry, of Thames Valley Police, described it as a "tragic case".
"On the morning of Monday 30 June, Liberty was looking forward to another day at school. Sadly her life was cut short due to the dangerous driving of Blackwell," she said.
"This case highlights the importance of driving safely and maintaining concentration at all times."
A man who killed a 14-year-old girl when his car mounted the pavement and hit a group of people has been sentenced to four years in prison.