West Nickel Mines Shooting. Several children were rushed to hospitals.Neighbors gather near a schoolhouse, seen in background, Monday, Oct. 2, 2006, where police say a gunman shot several people in Nickel Mines, Pa. A 32-year-old milk truck driver took about a dozen girls hostage in the one-room Amish schoolhouse Monday, barricaded the doors with boards and killed at least five girls and himself, authorities said.A law enforcement officer is shown at the doorway of an Amish school following a shooting in Nickel Mines, Pa., Monday, Oct. 2, 2006. To compile our dataset, we primarily relied on open-source databases, news reports, calls to police departments, information on school websites and 2009-2013 data provided by the Northwestern Institute on Complex Systems (NICO).Since there is no single definition for what qualifies as a school shooting, our team set the following parameters: The shooting must involve at least one person being shot (not including the shooter); and the shooting must occur on school property, which includes but is not limited to, buildings, athletic fields, parking lots, stadiums and buses. A 32-year-old milk truck driver took about a dozen girls hostage in the one-room Amish schoolhouse, barricaded the doors with boards and shot several people, killing at least five of the girls and then himself, authorities said.Law enforcement personnel carry a body bag out of a one-room Amish schoolhouse in Nickel Mines, Pa., on Monday, Oct. 2, 2006. There is no standard definition for what qualifies as a school shooting in the US. That's twice the average of the number of shooting victims at predominantly black and Hispanic schools.Mostly white schools also have more mass shootings, like the ones at Marjory Stoneman Douglas High School and Sandy Hook Elementary, typically carried out by young white males while school is in session.Experts say that while mass shootings are a concern, it's the day-to-day violence that impacts our schools more.“Those mass shootings, the headline-grabbing ones, are really, really a small fraction of them," says Cole.

While school shootings disproportionately affect urban schools and people of color, mass shootings are more likely to occur at white, suburban schools.With little federal data on school shootings, it’s hard to pinpoint what’s behind the recent increase.

But more often, they happen on Fridays.Experts suggest this could be due to tensions that build up over the course of a school week.“If something has transpired to bring you to the breaking point of committing some type of homicidal action … you may not have had any type of decompression time during the school week,” says Clumpner. That’s the disgrace.”Editor's Note: CNN spent more than a year analyzing the rising toll of America’s school shootings. Five girls died.A Pennsylvania state trooper leaves the schoolhouse where a gunman shot several students and himself in Nickel Mines, Pa., Monday, Oct. 2, 2006. On October 2, 2006, milk-tank truck driver Charles Carl Roberts opened fire on a small Amish schoolhouse in Bart Township, Pennsylvania. Without that research, we’re going blind into a “deadly future,” cautions Mark Rosenberg, who worked at the Centers for Disease Control and Prevention for 20 years and “You need those interventions that reduce gun violence and save lives, but that also protect the rights of law-abiding gun owners,” says Rosenberg. CNN will update its database throughout the school year, with 2019 numbers to come.CNN reviewed hundreds of reported shootings at K-12 schools from 2009 until 2018. They happened in big cities and in small towns, at homecoming games and during art classes, as students are leaving campus in the afternoon and during late-night arguments in school parking lots.CNN analyzed locations, time of day, type of school and student demographics to better understand how this trauma grips the country. Here are the 10 deadliest school shootings in American history: 10. Sept. 27, 2006: A 53-year-old gunman takes six girls hostage at Platte Canyon High School in Bailey, Colo.

It was a typical fall day. Authorities said the milk truck driver took about a dozen girls hostage in the one-room Amish schoolhouse, barricaded the doors with boards and shot several people, killing at least five of the girls and then himself.People kneel and pray on White Oak Road, Monday, Oct. 2, 2006, in Nickel Mines, Pa. A milk-truck driver carrying three guns and a childhood grudge stormed a one-room Amish schoolhouse, sent the boys and adults outside, barricaded the doors with two-by-fours, and then opened fire on a dozen girls, killing five people before committing suicide.A police helicopter takes off from the scene of a school shooting in Nickel Mines, Pa., Monday, Oct. 2, 2006.