(CNN) -- Children burst into tears in sixth-grader Nate Holley's classroom as gunfire erupted at his school Tuesday.
Two people believed to be students at STEM School Highlands Ranch had opened fire in two classrooms in the suburban Denver school.
"It was really chaotic," the 12-year-old said. "Most of the kids didn't know what to do."
Nate said he froze as gunshots shattered a window. A siren rang and someone in his classroom cracked a joke. His teacher shushed the student and moved them behind a desk and then to the closet.
"I had my hand on a metal baseball bat just in case," Nate told CNN's Brooke Baldwin. "'Cause I was gonna go down fighting if I was gonna go down."
Nate's wrenching account is a tragic reminder of what it's like to be a child in the United States in the age of school shootings.
Senior Kendrick Castillo was days away from graduation when he died lunging at one of the shooters. Eight other students were shot but survived.
Now, a community all too familiar with mass shootings is wavering between grief and gratitude over the fact that there weren't more victims.
Weeks earlier, Nate's school was placed on lockout due to threats targeting nearby Columbine High School, days before the 20th anniversary of the deadly massacre that took place there.
In 2013, the Arapahoe High School shooting prompted another lockout at Nate's school, his father, Steve Holley, said.
Tuesday's shooting marked the third time Steve Holley had to pick up his sons from school under these circumstances. But it was the first in which his own child was a direct witness to -- and survivor of -- such a tragedy.
"This community, in Colorado, we've been through so much recently," Steve Holley said.
"Enough is enough. We need to make a change and we need to do something or else we're just going to continue failing our kids."
As the situation unfolded Tuesday, Steve Holley shared on Twitter his experience of waiting to reunite with his children.
Fortunately, he knew early on that his sons were safe, he said.
A friend called to offer to pick up his other son "due to what was going on at STEM," Steve Holley tweeted.
Meanwhile, Nate had borrowed a cell phone and called his father from the classroom, he said.
"I told him to be brave," he said. "I told him I loved him and that I was on my way."
For nearly five hours, the Holleys waited with hundreds of parents at a recreation center to be reunited with his children.
He's grateful to law enforcement for their handling of the situation, but heartbroken by what his children and their classmates went through.
When asked about the decision to let his son appear on television, Steve Holley said he left it up to Nate, and Nate chose to speak.
"But I do feel it's important to hear not only from the adults but to hear from the kids," the father said.
™ & © 2019 Cable News Network, Inc., a Time Warner Company. All rights reserved.