Juvenile Court Judge William Schneider said he believes society's need to prevent such shootings outweigh T.J. Solomon's interests.
He ordered the case transferred to Superior Court, where Solomon could face life in prison if convicted of aggravated assault and other charges. The maximum juvenile sentence would have been 60 months.
Solomon, a sophomore at Heritage High School, is accused of opening fire May 20 with two guns in the commons area of the school 20 miles east of Atlanta. Six students were injured, the most serious a 15-year-old girl who spent almost a week in the hospital with a gunshot wound to the abdomen.
The judge's ruling came at the end of a three-day hearing.
Prosecutors said Solomon intended to hurt people, and should be tried as an adult. Defense attorneys Don Samuel and Ed Garland argued that Solomon is mentally ill and should be committed to a psychiatric hospital.
Garland said Solomon has the maturity level of an 11-year-old.
"Children require special care, they require special treatment and they require special punishment," he said. "If we send T.J. off to the adult system, perhaps we'll find him hanging in his prison cell one day."
A state investigator testified during the hearing that Solomon left a note referring to the shooting spree at Columbine High School in Littleton, Colo., that left 15 dead on April 20, exactly a month before the shooting at Conyers.
Schneider made note of that in his decision.
"The fact that the child has attempted to copy a heinous, premeditated crime and showed such disrespect for the safety of others ... makes the public's interest to treat him as an adult paramount to any interest of the individual child," he said.
Deputies immediately removed Solomon from the courtroom. He showed no response.
Defense attorneys may appeal the ruling to the Georgia Court of Appeals.
Michael Cheek, father of one of the victims, said he was pleased with Schneider's order.
"I think he made the right decision," he said. "(District Attorney) Richard (Read) said it properly. He sent a bullet through the hearts of this community and the entire country. Everybody's a loser with this one."