I personally fall somewhere in the middle. Bullying, however severe, is not an excuse for physical… — Sue Klebold

Dylan's struggles may have been hidden from us, but they were not uncommon ones. A 2011 study by the Centers for Disease Control found that 20 percent of high school students nationwide reported they had been bullied on school property in the thirty days before the survey; an even higher percentage reported they'd been bullied on social media. Anti-bullying advocates suggest the number may be closer to 30 percent. A tremendous amount of research has been done on the effects of peer harassment, and there is unquestionably a correlation between bullying and brain health disorders that stretches all the way into adulthood. A Duke University study found that, compared with kids who weren't bullied, those who were had four times the prevalence of agoraphobia, generalized anxiety, and panic disorder as adults. The bullies themselves had four times the risk of developing antisocial personality disorder. There is also a strong association between bullying and depression and suicide. Both being a victim and bullying others is related to high risks of depression, suicidal ideation, and suicide attempts. Researchers at Yale found that victims of bullying were two to nine times more likely to report suicidal thoughts than other children.

About five years after the massacre, I spoke with a Columbine High School counselor. He told me that, after an earlier, publicized bullying incident, the high school had implemented closer supervision of the student body, including teachers in the hallways between classes, and in the cafeteria at lunch. But we agreed it's impossible to control what two thousand students are doing on a campus- or to know what those kids are doing to one another in the Dairy Queen parking lot. Despite the administration's claim that steps were taken to stem conflict among students, their efforts fell short. For many people, Columbine High School was a hostile and frightening place even if you were one of the most popular kids, and Dylan and his friends were not. One of our neighbors told us her grown son's reaction to the tragedy, a refrain we heard many times: "I'm just surprised it didn't happen sooner."

The connection between bullying and violence toward others is more complicated, although again there's a correlation. Bullied kids often become bullies themselves, which appears to be what happened with Dylan and Eric. Larkin cites a student who claims they terrorized her brother, a student with special needs, so badly he was afraid to come to school. Researchers call students who both bully and suffer bullying "bully-victims," and find that these bully-victims are at the greatest psychological risk. "Their numbers, compared to those never involved in bullying, tell the story: 14 times the risk of panic disorder, 5 times the risk of depressive disorders, and 10 times the risk of suicidal thoughts and behavior.