The boy's attorney indicated they plan to appeal.
Stevens County Prosecutor Tim Rasmussen asked for an exceptional sentence that would have put the boy in custody until at least the age of 16.
The boy pleaded guilty just before the start of his trial in April. He was charged with conspiracy to commit murder, juvenile in possession of a firearm and witness tampering.
The second defendant in the case, an 11-year-old boy, remains in custody.
The two fifth-graders were arrested Feb. 7 after officials discovered them trying to sneak a gun and knife into their school. Police interviewed the boys, who confessed they had been planning on attacking a classmate that same day.
The boys were expelled from school.
The 11-year-old boy is currently having his mental competency evaluated by doctors at Eastern State Hospital. The tests will evaluate the boy's sanity and his fitness to stand trial.
Dr. Kevin Hyde addressed Wednesday's sentencing hearing by phone, saying that he had met the 10-year-old boy for three sessions and felt he was not a high risk to commit violent acts. Hyde said the prosecution sentencing recommendation was inappropriate.
"I think it would be wrong to incarcerate this child until the age of 16. We don't need to ruin this child's life," Hyde said.
The mother of the girl who was the target of the boys' attack said her daughter forgave the boys, and asked for a sentence of longer than two years.
Rasmussen, in seeking an exceptional sentence, said the boy "was dangerous on Feb. 7 and he's dangerous today."
"He doesn't think in terms of how his actions affect other people. There's something missing in him," Rasmussen said, adding that the boy's thinking was "like a video game. There's someone in your way, you kill them."
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