The messages "detailed a school bombing and school shooting" at the Roy Brown Middle School last Friday, Detective Lt. William Duran said Thursday.
A shelter-in-place immediately went into effect at the Washington Avenue school that day after the messages were received, Duran said.
The Bergen County Sheriff's Bomb Squad and K9 Unit were among the responders.
"A sweep of the school and search of the juvenile's home were conducted with nothing found to indicate a threat to the public," Duran said.
The shelter-in-place was lifted an hour and 10 minutes after it began, he added.
Police signed delinquency complaints against the youngster charging him with two counts of making terroristic threats and one of making a false report, the lieutenant said.
He was released to his parents pending a closed-door hearing in the Family Part of Superior Court in Hackensack.
Click here to follow Daily Voice Bergenfield and receive free news updates.