Lindop School in New Hampshire was evacuated after a gunman opened fire at the school, killing two students and a teacher.
A second shooter is believed to be holed up in a house in the neighborhood.
Police found the gunman, who has not been identified, and the school was locked down as a precaution.
“There is no evidence to indicate that this was a random act,” Superintendent Thomas O’Neill told reporters.
Lindop, which is located on Route 30 in New York’s Catskills, is the only elementary school in the district that is open on Fridays and Saturdays.
A day earlier, two students were killed in a separate shooting at Lindop, a town of more than 13,000 people about 50 miles north of Syracuse, New York.
The shooting at the New Hampshire school came after a week of heavy snowfall that forced the cancellation of an upcoming holiday parade.
The school reopened on Friday, with students back in classes.
Students from both schools were being reunited, and many parents were in the crowd to greet their children.
Lindo’s parents, Fred and Rose Lindop Jr., were in New Haven, Connecticut, for a holiday family reunion on Friday.
“We want to thank the parents and teachers who came to see us, and we also want to give our condolences to the Lindo family, who are devastated by this terrible tragedy,” the school’s principal, Laura Schaffer, said.