In a deal with prosecutors, adult charges, which included attempted aggravated murder, were dropped. Grant Acord, 17, admitted to six counts of manufacture of a destructive device and two counts of unlawful use of a weapon.
Citing the results of a psychological evaluation, which were not disclosed, prosecutors, the judge and defense attorney agreed the matter appropriately belonged in juvenile court.
"The potential act is very alarming to the public," said Judge Locke Williams. "I think given the heightened awareness of mental health issues and the effect that mental health issues can have on youth in particular, that we're very fortunate, and I think we owe a debt of gratitude to the young man who brought this to law enforcement's attention."
Police arrested Acord last year after receiving a tip from a West Albany High School classmate. He wrote detailed plans to "shoot and throw bombs throughout the school" and then kill himself, authorities said.
The plans, which included a step-by-step itinerary for an attack, were written in notebooks that were found hidden beneath the floorboards in the teen's bedroom, along with two pipe bombs, two Molotov cocktails and at least two Drano bombs, police said last year.
A detective wrote that the notebooks indicate Acord "compares himself to both Eric Harris and Dylan Klebold," the teenagers who killed 13 people at Columbine High School in Colorado in 1999 before turning their guns on themselves.
Wearing a plaid shirt and khaki pants, Acord responded "yes, your honor" and "no, your honor" in response to questions from the judge. He declined an opportunity to say more.
Before reaching a deal with prosecutors, Acord had been planning an insanity defense. His defense attorney, Jennifer Nash, had argued that Acord can distinguish right from wrong, but he was unable to follow the law because of a mental disorder.
After he was arrested, Acord's mother, Marianne Fox, released a statement saying her son has a rare form of obsessive-compulsive disorder.
In Oregon juvenile court, youths accused of wrongdoing do not enter pleas or receive convictions.
The Associated Press normally doesn't name minors accused of crimes, but it is doing so in this case because of the seriousness of the allegations and because Acord was initially charged as an adult.