The body of Colleen Ritzer, 24, was found in the woods behind the school. The suspect was not named because of state law concerning minors.
The suspect was reported missing Tuesday when he did not come home from school. Ritzer was reported missing about 11:20 p.m., when she did not return home or answer her phone.
Police searched the school and found blood in a second-floor bathroom. They found her body behind the school later that evening.
“She was a very, very, respected, loved teacher," said Essex County district attorney Jonathan Blodgett. "It’s a terrible tragedy for the entire Danvers community."
Police found the suspect at 12:30 a.m. Wednesday walking on the side of the highway. He will be arraigned later today in juvenile court.
Blodgett said authorities have not yet decided whether he will be tried as an adult in the murder.