Like many teenage girls, Rachel Scott kept a diary. Inspired by Anne Frank, she wrote of her desire to start "a chain reaction of kindness that would ripple around the world". She might well have grown up to pursue her compassionate vision. But on 20 April 1999, two boys went on an armed rampage at their high school in Columbine, Colorado, killing 12 students and one teacher before committing suicide. Rachel was their first victim.
In the days after the massacre, Rachel's father Darrell heard many stories of his daughter's kindness. She had befriended a lonely new girl whose mother had died in a car crash. She protected a disabled boy from bullying. Against the horror of that day, Rachel's life offered a powerful counterpoint.
Today, her story is the focus of a burgeoning anti-bullying movement. Rachel's Challenge, founded by Darrell Scott, sends speakers into schools across America to inspire other children to follow Rachel's lead. They show news clips of Columbine and re-enactments of Rachel's good deeds, and then set a series of challenges, from choosing positive influences and dreaming big to looking for the best in others, eliminating prejudice and implementing Rachel's "chain reaction of kindness".
"It's a very emotional experience for the kids," Scott says. "We see a huge number with tears running down their faces, hugging each other, asking forgiveness."
Last year alone, two million students in 1,600 schools took part in the programme. This year it will be closer to three million. Scott and his team of 44 presenters struggle to keep pace with demand. Bullying is rife in American schools, in the classroom and increasingly online. The suicide of college student Tyler Clementi last September prompted renewed calls for action. Rachel's killers, Eric Harris and Dylan Klebold, were themselves believed to be victims of bullying, as is Jared Loughner, perpetrator of the US's latest bloody tragedy - the shooting of congresswoman Gabrielle Giffords.
Scott receives dozens of emails each month from bullied children who say Rachel's Challenge has literally saved their lives. "I was so depressed that I wanted to kill myself," writes KC from Colorado. "I would shoot myself with a gun on Monday 25th. But that day Rachel's Challenge came and spoke to my school. Now I know that I can make it through."
Harrison High School in the state of New York hosted the presentation in November. Assistant principal Josh Elder says the response was "tremendous". Over 250 students have formed a Friends of Rachel club to change the school culture. They started a committee to welcome new students and a letter-writing campaign to thank the lunch staff, janitors and security staff.
Creating that desire for change is the key to success, Scott says. "The focus shouldn't be on trying to get kids to not be bullies. The goal should be what you want them to be, not what you don't want them to be.
"We go to the worst schools in America, to the Bronx and gangland areas of Houston and San Diego, but we never have a discipline problem because the story bypasses their brains and hits them in the heart."