Family members of one of the Leeds Stonegate Road victims reacted with anger as the judge told a court the teenager would be released on licence after serving half of his sentence.
Outside Leeds Crown Court, the sisters of Darnell Harte, the 15-year-old killed in the crash, claimed the sentence was “not justice”.
One sister said: “In two years’ time he’s going to be out and we’re going to have to see his face and not say anything because he’s served justice in some people’s eyes - to me that’s not justice, because I’m never going to see my little brother ever again.
“He was the best brother you could ever have.”
The Recorder of Leeds, Judge Peter Collier, QC, said an adult defendant would have been sentenced to almost 14 years for the offences if convicted after a trial.
The judge said he had to take guidelines relating to the punishment of young people into account when sentencing the defendant.
He said: “Some of the things I have to bear in mind are the seriousness of the offence.
“The other part of seriousness is what Parliament calls culpability, which means the amount of blame that you should carry for what happened.
The judge added: “I must also have regard to your welfare, so it is an individual approach, and also to what is said to be the principal aim of the youth justice system, namely to prevent re-offending.
“That is a long list of things which I have been thinking long and hard about.
“The hardest of those things to do is assess what your real age is in that wider sense that includes your developmental and emotional maturity.”
The judge said he had read reports that the teenager had missed school because of medical problems and was at the level of a 10-year-old child.
He continued: “In light of all that I know about you, it is clear that I must reduce the adult level of sentence by quite a lot.”
The judge said the teenager was also entitled to a reduction in his sentence because of his early guilty pleas.
An application to lift reporting restrictions on naming the boy was also refused by the judge.
He said: “Many people know who you are, particularly the families of those who died.
“But I cannot see that it is in the wider public interest that people who don’t know you should be told your name.
“You know what a dreadful thing you did and...I am quite sure that that night will forever shape your life.”