Ron Edwards, principal of the Bethel, Alaska school for four years, was killed by a student armed with a rifle and revolver.
Another student was fatally shot and two others were wounded when Evan Ramsey went on a 20-minute shooting spree.
Teachers tried to talk him into dropping his gun. The violence ended in his arrest after an exchange of fire with local police.
Ramsey was a loner whose father had a criminal history, students said. He had talked of bringing a gun to school and shooting the headmaster, but no one took him seriously. He ambushed Mr Edwards in a hallway.
His second victim, John Palacious, was known as a popular figure at the 400-student school, who had sometimes teased Ramsey.
Nearly one in 10 American teachers report being attacked in school, with almost all the attacks carried out by pupils. A recent survey suggested that as many as one in five American high-school students has access to a gun.
Mr Edwards joins a list of teacher casualties from firearms. Last year, Los Angeles teacher Alfredo Perez was hit in the head in the crossfire from a gang shooting. In Washington State, also on the Pacific coast, another teacher was shot dead.