On April 20, 1999, Craig Scott was applying hair gel when his older sister, Rachel, called to him from the kitchen: “C’mon! We’re going to be late!” As they climbed into her red Acura and headed to Columbine High School, their annoyance was mutual. The siblings loved each other but were…different. Craig was 16, an athlete who tried to fit in with the cool kids. He was often late. Rachel, 17, loved her church youth group and was always punctual. When she tuned the radio to a Christian station, Craig abruptly changed it to rock, and as they arrived at school, he slammed the car door without saying good-bye.

Several hours later Craig was studying in the library when teacher Patti Nielson ran in, shouting, “Get under the tables, kids!” Everyone looked around at first, suspecting a prank. Just then, a student stumbled through the doors and collapsed. Craig and his friends Isaiah Shoels and Matt Kechter clambered under a table. He heard Nielson talking on a school telephone, telling emergency dispatchers there was a shooter roaming the halls. Then he heard the doors open. “Oh God,” the teacher said. “He’s right there, he’s in the room.” The “he” was actually them: Eric Harris and Dylan Klebold.

When Craig, a wrestler, heard Klebold and Harris talking about targeting anyone with the white hats often worn by athletes, he shoved his baseball cap under his shirt. Amid the echoing gunfire and the whimpering of other students, he squeezed his eyes shut and prayed as one of the gunmen drew near and yelled, “We have a nigger over here,” referring to Shoels. They fired off more racial slurs and then shot both of Craig’s friends to death. Possibly because he appeared dead, they left Craig unharmed. He soon fled the library, where 10 victims had been killed, and emerged to horrific news: Rachel had been the first student murdered. She was eating lunch outside when the killers approached the school building and shot her on their way in.

Rachel’s bedroom soon became a place for reflection. For months afterward, some members of Rachel’s family—she left behind a mother and stepfather, father and stepmother, and four siblings between the ages of 14 and 23—would wander into her bedroom at her mother’s house to think about her, to talk about her, or simply to cry. One afternoon Rachel’s father, Darrell Scott, and Bethanee, her oldest sister, found a graded essay called “My Ethics, My Code of Life” tucked under her mattress. I have this theory that if one person can go out of their way to show compassion, then it will start a chain reaction of the same, she wrote. People will never know how far a little kindness will go.

The family eventually found a half-dozen more journals, including two that were in her backpack when she died. Many of them were filled with prayers expressing a fervent desire for her life to somehow help others, and several passages were hauntingly prescient: This will be my last year, Lord. I have gotten what I can. Thank you, read one entry from May 1998. Rachel’s sister Dana, then 22, recalled Rachel once mentioning that she thought she would die young, but Dana wrote it off as a comment made by a theater-loving teenager with a flair for drama.

The Scotts started to hear stories about Rachel from her friends. One girl told them how Rachel invited new kids to sit with her and her friends at lunch; a special education student described the time Rachel stopped some boys from mocking him. During this time, Darrell gave media interviews about Columbine and spoke publicly about the ordeal; his talks always focused on Rachel’s essay, on kindness and compassion starting a ripple effect. The more he told his story, the more requests he received, primarily from colleges and youth organizations. But he soon realized the best way to memorialize Rachel and prevent the kind of violence that took her life would be to focus on schools.

Darrell founded Rachel’s Challenge in 2000 as an educational nonprofit. He delivered his first presentations to students in El Paso, Texas, where he knew people involved with the local school system. Soon he was telling school assemblies across the country about Rachel’s life, death, and writings. Today, as the 14th anniversary of the Columbine shootings draws near, Rachel’s Challenge has become the largest school assembly program in the United States. More than 50 full- and part-time presenters, including Craig, use anecdotes and video clips to remember the Columbine shootings and share Rachel’s message that selfless acts such as reaching out to lonely peers, reconciling with estranged friends, or refusing to be a bully can prevent violence and suffering. The organization supplements the assemblies with 27 programs that include exercises designed to combat low self-esteem and help students see what they share instead of what separates them. Scores of schools have also started Friends of Rachel Clubs, which conduct everything from graffiti cleanup and hurricane relief efforts to recognition days for teachers, janitors, and librarians. (Dana, now 36, is a Friends of Rachel Coach.) Most recently, Darrell has begun training teachers in the new programs. “Rachel is the heart of our organization,” Dana says, “but my father has been the head and hands.”

The results have been impressive. Participating schools have reported substantial declines in disciplinary actions such as suspensions and expulsions. Rachel’s Challenge has received more than 500 unsolicited emails from students who say they were considering suicide until they heard Rachel’s story. There also have been at least six school shootings that were averted following assemblies, often because students overheard peers discussing violent plans and alerted school authorities.

Craig, a national spokesperson and frequent presenter for Rachel’s Challenge, had an especially chilling experience after one assembly in Texas. During his presentation, he’d noticed an angry-looking teenager dressed in black in the audience. He told himself, If I can reach that kid, I’ll reach everybody. Afterward, the teen approached Craig and handed him a hit list. “You just saved a lot of people,” the boy said before turning himself in to school authorities.

On the morning of Friday, December 14, 2012, Darrell and Craig were concluding a presentation in a downtown Denver boardroom when their cell phones started buzzing. They’d just explained how, out of respect for the other Columbine victims and families, they waited about 10 years to introduce Rachel’s Challenge to Colorado, when the grim news arrived: A gunman had fired a barrage of bullets into Sandy Hook Elementary School in Newtown, Connecticut, killing 20 first-graders and six staffers.
Father and son and their team began fielding calls from media outlets. As a survivor of one of America’s most notorious modern-day school massacres, Craig has become an “expert” every time someone walks into a school and opens fire. He returned to his downtown loft to prepare for interviews on shows including Dateline NBC, Nancy Grace, and Katie. “I’ve done this at least 10 times,” he said. “The Amish school shootings, Virginia Tech…but this is the worst.”

In jeans and a collared shirt, he sat at a table, gazing out the window at the skyline while two cameramen set up lights in his living room. He looks much like he did at 16, although sharper facial features give him a serious, purposeful confidence that’s absent from his high school pictures. “I think about what’s different about this generation than in my father’s generation,” he said. “No one from my father’s generation would have done this.” His theories include everything from the erosion of families and tight-knit communities to easy access to military-style guns and the ubiquity of violent movies and video games.

Minutes later, he conducted a Skype chat with an Atlanta NBC affiliate. “I don’t think Rachel’s Challenge is a solution to everything, but we do believe in affecting culture through kindness and compassion,” he told the reporter. “[These incidents make us] even more resolved to do what we do.”

It’s easy to wonder how he can keep retelling his story—he’ll give some 50 speeches this year. At first it was therapeutic, a way to survive his own trauma by helping others with theirs. Now that he’s recovered from the grief, flashbacks, and nightmares of April 20, 1999, retelling it has become tougher, a constant revisiting of a place he’d rather leave behind. Even so, his determination to honor his sister’s memory hasn’t waned. “Columbine was the worst day of my life,” Craig says. “But I found my greatest purpose from that pain. I don’t like reliving that experience, and I don’t necessarily even like talking about it. But I like the impact it has, the difference it makes. My job is to change people’s hearts, and that’s a pretty cool job.”