Soon, though, students learned no one else was in danger. One of their eighth-grade classmates had taken his own life, shooting himself in the head with a handgun in the hall, authorities said.
"Throughout the entire thing, we all thought someone shot someone else," said student Paiton Gardner, 14. "We didn't know it was a suicide. We were freaking out."
Some students bolted outside Stillwater Junior High. Staffers quickly locked down the building and evacuated the rest of the school's 700 eighth- and ninth-graders, along with students from an adjacent elementary school, police Capt. Randy Dickerson said.
Dickerson said the 13-year-old didn't leave a note, and authorities said they don't know why he killed himself. Superintendent Ann Caine, who oversees the district about 70 miles west of Tulsa, said there weren't any reports that the teen had been bullied.
"There is no indication that that's what occurred," Caine said. She said the teen was a good student who got along with other kids.
Police wouldn't say where the weapon came from or how the eighth-grader got it into the school. Caine said there aren't any metal detectors but expects there will be discussions about the policy.
Gardner said she realized something was wrong early Wednesday when students began to run past her.
"People looked terrified," said Gardner, a ninth-grader. "The football coach was like, `Get out, get out! Someone's been shot."'
She and other students sprinted down the hallway, passing blood on the wall and floor as she ran to a nearby playground.
Another ninth-grader, Jake Green, said he heard the single shot ring out after he and dozens of other students gathered to pray before school.
"We heard this loud boom and everyone just got quiet," Green said. "No one said a word."
A teacher told the students to get out of the building, Green said.
"Everyone was really scared. We didn't know if the kid shot himself or if there was a shooter outside the school who shot in," Green said. "Everyone didn't know what was going on, so they were screaming and running as fast as they could to get to the playground."
Some students wore superhero costumes Wednesday as part of an effort to raise cancer awareness, but Dickerson said the student who shot himself didn't appear to be dressed up.
"If was wearing a costume, it wasn't evident to me," Dickerson said.
Green said students who were already in their classrooms were locked in the building for about an hour. Parents were told to pick up their children at a nearby shopping center.
"It was really scary," Green said. "Everyone's kind of traumatized and doesn't know how to act or respond."
Some people planned to gather to pray Wednesday night at the nearby Highland Park United Methodist Church.
The Rev. Derek Belase said he doesn't know the teen's family.
"We do know that they're hurting," Belase said.
Kenny Monday told The Associated Press that his son, Kennedy, heard the gunshot but did not witness the shooting.
"It's so sad that the kid lost his life, but we're just glad he didn't shoot anyone else," Monday said.