She was killed nearly 10 years ago in the worst mass high school shooting in U.S. history, but Columbine student Rachel Scott's message of kindness and compassion reached a brand new audience of teenagers on Monday.

"She was a spark plug," her father, Darrell Scott, told an auditorium packed with 1,400 students at Castle View High School in Castle Rock. "She challenged people to start a chain reaction of kindness and compassion . . . (but) Rachel had no idea, 10 years after her death, she would be sharing her story with the world."

The anniversary of the shootings is April 20. Scott, 59, has made his late daughter's story an international movement, reaching millions of people worldwide through books, films, documentaries, TV shows and speeches.

Scott urged the Castle Rock students to take up "Rachel's Challenge," a list of good works that the teenager stressed in her diaries, including the call to eliminate prejudice, dare to dream, become a positive influence on others and reach out to the disaffected. The two Columbine killers had few friends and immersed themselves in violent movies and video games.

Scott told the students how Rachel's brother, Craig, who "stared down the barrel of a gun" that day, battled back from severe depression to begin his dream of producing quality, positive-minded films.

There were soft gasps from the crowd as Scott shared how Rachel's diaries - one found in her bullet-riddled backpack - contained uncannily prophetic writings about her belief that she would die young but have an impact on the world: "This will be my last year, Lord," she wrote, shortly before her death.

Despite examples of Rachel defending disabled students and befriending the lonely, her father added, "She would want me to say this - she was not perfect. She said, 'I fell a few times but I didn't give up.' (Now) I challenge you never to give up."

After the gathering, some students came up to Scott in tears, some to thank him. Kristle Wiles, 16, told Scott his message was especially timely, coming after the recent suicide of a student who had come across as "different." The student had seemed outgoing, Wiles said, but it was later discovered she was depressed - someone who might have responded to Rachel's brand of kindness.

Scott's talk, Wiles said, "opened our eyes to what was actually going on in our lifetime."

At the time of Rachel's death, Scott was in sales and marketing for a food company. His first public appearance after Columbine was testifying before Congress about school violence.

From there he began his motivational business to tell Rachel's story. It now employs 50 people. He declined to say how much he earns, but added, "I don't make any more than a school superintendent makes, but I work harder than they do."

Castle View High Principal Lisle Gates said Scott's daylong appearance was free - it was his second at the school - because Scott's stepson, Ryan Hollingshead, is Castle View's football coach.

Scott also held a voluntary, afternoon training session for interested students to take part in Friends of Rachel, a club to put words into action, and an evening seminar for parents and the public.

The afternoon training was so packed, the school announced by loudspeaker that no more students could be admitted. Scott told the group, "You're here for one reason - not to skip class or be with your buddies . . . your reason to be here is to build a better school and community."