The children were 5, 8 and 11 years old. Two other people, a 7-year-old and another teacher, were critically injured.
All of the victims were shot in one classroom, which was a special needs classroom, officials said.
The suspect, identified by police as Griffin J. John II, was a 16-year-old Bend resident. He was armed with a long gun and gained entry into the school by shooting through locked doors, officials said.
The gunman was killed by a community member, according to authorities, who credited him with preventing further loss of life. The man’s brother identified him as Kaylub Giamanco, a father of two students at the school who heard the gunshots while driving home.