Frank Fechteler, who attended Newington High School, was charged late Wednesday and ordered held in lieu of $500,000 (EUR 380,604) bail, state prosecutors said. He was arraigned Thursday in juvenile court.
Police said they seized weapons from Fechteler's home after receiving a tip from a parent about the attack plan.
The plot was foiled when a teen who knows the suspect sent a link to an Internet video on YouTube.com to a person who did not know Fechteler, police said. The video showed area high school students firing weapons and igniting explosives, but it was unclear Thursday who had made the video.
The teenager who received the link shared the information with a parent, who contacted police.
"We are extremely grateful that this parent took the important step," Newington Police Lt. William Darby said. "We believe this was a legitimate threat."
Police interviewed the students and learned that Fechteler planned to carry out the assault. The investigation determined no other students were involved.
Parents of students identified as targets of the plot have been notified.
Prosecutor Kathleen McNamara and public defender Christopher Eddy declined to comment on the court appearance Thursday. Authorities said the teen continued to be held, the AP reports.
His parents, William and Soon Fechteler, declined to comment after the court appearance.
Newington police said that Fechteler underwent a psychiatric evaluation and that his family was fully cooperating.