Two teenagers killed a teacher and a dozen fellow students in Colorado's Columbine High School, and wounded two dozen others, before committing suicide.
But survivors have gone on with their lives.
Patrick Ireland was the student seen in a famous video being pulled from a window in the midst of Columbine's chaos.
His fight to overcome the unthinkable still stands out.
"My entire instincts," he now tells CBS News correspondent Mark Strassmann, "were for survival. Just get out."
The Columbine killers left Ireland in the library, shot twice in the head.
Partially paralyzed, delirious, he willed himself toward the window.
"My entire crawl was filled with adrenaline and fear -- the fact that they might come back in, and kill me."
He had to learn to walk and talk again.
But graduated valedictorian of his Columbine class.
Then, Ireland got married, and is now a financial planner.
"I'm not going to allow that event to define who I am as a person," he vowed to Strassmann.
Craig Scott was also in the school library that day, and his sister, Rachel, was the first student killed.
On The Early Show Monday, Scott told co-anchor Harry Smith he's "taken what's happened, and taken the story of myself and my sister into schools with a program that my family started, called Rachel's Challenge. And we've seen an immense amount of good come from that program, and so it is a day I think about constantly since it happened.
"It's changed my life and changed who I am. It's made me a deeper, stronger person, and I've been able to focus on something that was positive since the shooting happened - my sister's story. My sister, you know, the Columbine shooting happened, and it was a very angry, hateful thing that the two shooters did, and I feel like an antidote to anger and hatred is kindness and compassion."
"The embodiment of your sister," Smith remarked.
"And actually," Scott continued, "seen some school shootings stop from happening since then. So, that's one of my life's work; (it's) what I do."
Lauren Beyer-Bohn, who was a 15-year-old freshman that day, told Smith her "biggest mission has been taking this tragedy and turning it into a triumph, as far as taking something that was so terrible and horrible and turning it around into something positive. And I know Craig feels the same way, as far as seeing how the stories of the survivors and the stories of the people that lost their lives can really make us appreciate each and every day that we have.
"It's empowering to say that I have survived a situation, and have been able to take our stories and messages across the nation, and bring hope to a lot of people."