Alongside the tragic toll of school shootings from Columbine to Virginia Tech to Newtown, Conn., stands another list that offers some hope.
More than 120 attempted or planned assaults on schools nationwide were halted by authorities without loss of life by students or school staff, including three in Arizona.
See our interactive map of the school locations embedded below.
The list, compiled between 2000 and 2010 by Cleveland-based National School Safety and Security Services, is based almost entirely on contemporary media reports. It is not comprehensive, but represents a sampling of what were likely many hundreds more unpublicized threats blocked before harm could be done.
"The good news is that schools have become much better at averting these incidents since Columbine and Sandy Hook,'' said Ken Trump, president of the school security consulting group. "The bad news is that we will always have incidents that will slip through the cracks when you're dealing with human behavior."
"I daresay there are many more instances that have occurred around schools that never get reported publicly for various reasons,'' added Mo Canady, executive director of the National Association of School Resource Officers, which supports law enforcement officers assigned to schools.
A review of the 121 incidents shows the majority of threats to the schools involved actual or intended use of guns (55 instances) or explosive devices (22), with the rest not specified.
The reports indicate most of the threats were blocked by police investigations or law enforcement interventions at the schools when an assault was already underway. School administrators, counselors, school resource officers, even janitors and cafeteria workers, foiled at least 19 threats.
In Olive Hill, Ky., early in 2002, a 12-year-old middle school student briefly held another male student hostage at gunpoint in a hallway. The school resource officer was able to end the incident without any injuries.
In September 2006, a student told a school resource officer in Green Bay, Wis., that two 17-year-olds planned an attack at the school. A search of one of the boys' homes found sawed-off shotguns, pistols, ammunition, several bombs, bomb-making material, camouflage clothing, helmets and gas masks.
"The dynamics of schools' response to the threat of violence has changed since Columbine (the Colorado high school where two seniors murdered 12 classmates and a teacher before killing themselves April 20, 1999)," said Curtis Lavallo, executive director of the School Safety Advocacy Council, a consulting and lobbying group. "There's no longer just one person in charge of safety at a school, but a whole team of folks that extends out into the community."
In Spokane, Wash., in 2005, a 14-year-old boy expelled from high school for writing a threatening note to his teacher had written a suicide note and was headed for the school with a loaded handgun to shoot the teacher when family members found the note and called police. They were able to apprehend him when he was about four blocks from the school.
The next month, in Ashville, N.C., an 8th grader posted an Internet threat: "I'm planning a Columbine on my dumb hippie school on the last day of school so everybody will be there to enjoy the Massacre." Later, he allegedly added, "I know where my dad's 12-gauge is along with his .45, .38 and his .22." An adult in Ohio read the posts and reported the threat to authorities in North Carolina.
The records also show that attempts at school violence tend to increase in April around the anniversary of Columbine. "There are peaks and valleys in reporting, particularly after an actual attack, ‘' said Katherine Newman, a professor of social sciences at Johns Hopkins University who has studied mass school shootings, including some she terms "near-miss" cases. "The sensitivity that this could really happen here goes up, although it may not be sustained over time."
Canady said even though the unlikelihood that mass violence will strike any given school, police officers and administrators have come to treat all threats more seriously.
"Whether it's something a student hears or someone sees on Facebook, whatever it is, it's more apt to bring the attention of police officers."