Baldwin fell silent and threw her hands up.

“You were going to go down fighting with a baseball bat,” she repeated slowly. “And again, Nate, how old are you?”

“I’m 12 and a — " Nate paused before finishing the phrase. “I’m 12.”

The moment resonated on social media after one student was killed and eight others were injured in a shooting Tuesday at STEM School in Highlands Ranch, Colo. People across the country expressed horror that a child still young enough to think of his age in half-years was calmly explaining how he had prepared to fight for his life while hiding in a classroom closet. How on earth, people asked on social media, did we get here?

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Some people bemoaned Nate’s apparent loss of innocence; others said the video segment was proof that American society had failed Nate and other kids like him. One person said he looked “impossibly young.”

“Innocence shouldn’t collide [with] a need for that bravery at 12 yrs old,” tweeted former MLB player Michael Young.

“'Be brave,' we tell our children. But what we are asking of this generation is insanity,” a foreign policy consultant posted.

“Is this what we’ve become?” asked a pediatrician in Missouri. “A nation that relies on our children to lay down their lives for one another as we do nothing? Not ok.”

A student laid down his life for his classmates just last week, in fact, when a 21-year-old student at the University of North Carolina’s campus in Charlotte knocked down a gunman in his classroom. Police said the student, Riley Howell, was key to the assailant being disarmed. Howell and fellow student Ellis “Reed” Parlier, 19, died in the attack.

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Active shooter trainings have become much more frequent at schools nationwide in recent years, reflecting a student population that has come to know mass gun violence as the new normal. More police officers patrol schools, and some districts let teachers carry guns for security.

Ken Trump, president of the consulting firm National School Safety and Security Services, said many students who experience shootings already deal with the high anxiety levels that have become common among preteens and teenagers. This worry, Trump said, makes students inclined to prepare to protect themselves and others when an active shooter is in the building.

“I think we’re somewhat creating this,” Trump said, by spreading conflicting information during school safety planning. Districts often struggle to decide whether to focus on lockdowns, mental health, security cameras or other tools for dealing with such shootings, he said.

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Michael Dorn, executive director of the nonprofit campus safety group Safe Havens International, cautioned that fighting a gunman who has not yet shot his weapon could backfire and cause him to shoot. Students and staff should be aware of unusual behavior before a shooting ever begins, Dorn said, and seek safety and alert authorities if they sense danger.

Still, Dorn said, it does not hurt to figure out potential escape methods while a shooting is happening. “You should be thinking ahead of what might happen next,” he said. “That will increase your chances of survival.”

At Nate Holley’s school, he said, most kids did not know what to do when gunfire broke out. They had done one or two lockdown drills this school year, Nate told CNN, but chaos took over when the shooting began. At least half of the students in his class started crying, he said.

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“I have sensitive ears, so they shot out the doors, and I heard the gunshots and I just kind of froze,” Nate said.

His teacher, he said, moved the class behind her desk and then into the classroom’s closet. Nate said he was hiding in a corner while the gunman stood right outside the door.

“This is the third time I’ve had to pick up my kids from a lockdown at their school due to a school shooting or the threat of a school shooting,” Nate’s dad, Steve Holley, told CNN.

“Bomb threat,” Nate added, apparently indicating that a bomb threat may have been the reason for one or more of those lockdowns.

Holley pointed to a shooting at Arapahoe High School in Centennial, Colo., that killed one student in 2013. And last month, around the anniversary of the 1999 massacre at Columbine High School, a woman flew to Denver, bought a shotgun, obsessively studied the Columbine shooting and then killed herself in a remote mountain area.

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“This community out here in Colorado, we’ve been through so much recently,” Holley told CNN.

He posted on Twitter to thank the parents of 18-year-old Kendrick Castillo, a senior at the school who reportedly lunged at the shooter and tried to grab his gun. Castillo has been credited with giving other students the chance to run or hide under desks. Holley wanted to say “I’m sorry” and “thank you” to Castillo’s parents, he wrote, in equal measure.

Perry Stein contributed to this report.