The sentence handed down by McCracken Circuit Court Judge Jeff Hines was the stiffest available to him under Kentucky law for a minor.
Carneal pleaded guilty but mentally ill in October to the December 1, 1997, shootings. His lawyers said Carneal suffers from depression and a schizophrenia-like disorder.
Carneal had repeatedly fired a .22-caliber semiautomatic pistol at a prayer group during a rampage at Heath High school. One students was left paralyzed from the chest down.
One report made public in the months since the shooting quoted Carneal as telling doctors: "I regret what I did. I know I killed people. It wasn't right...I have no explanation for what I did."
He also told of stealing two guns from his father, saying that "more guns is power. You have more power. You look better if you have a lot of guns."
He said he thought his fellow students, many of whom had ignored him, would be impressed by the guns.
"I don't know why I wasn't bluffing this time," he said." I guess it was because they ignored me. I had guns...I thought they would be scared and then no one would mess with Michael...they would talk to me and things would be different."
The Paducah school shooting occurred two months after one in Pearl, Mississippi, and was followed by similar incidents in Arkansas and Oregon that prompted a national debate about school safety and gun control.