Dylan Klebold (R) and Eric Harris are shown in the Columbine High School cafeteria on the day they killed twelve students and one teacher before killing themselves on April 20, 1999, in a still image from a security camera
Killer: Seung-Hui Cho (committed suicide)
Cho's rampage is considered the deadliest shooting by a single gunman in U.S. history and raised questions about how someone known to be mentally ill could buy firearms. The school was found guilty this year of negligence in a civil suit filed by parents of two students killed.
Aug. 1, 1966
University of Texas
Killer: Charles Whitman (died in the attack)
After killing both his wife and his mother at their homes, Whitman went on a 90-plus-minute shooting spree from atop an observation deck at the school before being shot by police.
April 20, 1999
Columbine High School
13 dead: 12 students, 1 teacher
Killers: Dylan Klebold and Eric Harris (died in the attack)
The pair went on a spree through the halls of the school armed with guns, knives and bombs, and were among the bodies pulled from the building. Much was said about the boys' perceived alienation and alleged interest in dark music like Marilyn Manson.
July 12, 1976
California State University, Fullerton
Killer: Edward Charles Allaway
Allaway, a custodian at the school where he committed mass murder, remains in a psychiatric hospital in California.
Oct. 2, 2006
West Nickel Mines School
Nickel Mines, PA
5 dead, all girls aged 6 to 13
Killer: Charles Carl Roberts (committed suicide)
Roberts allowed some of his hostages -- a pregnant woman, three parents with infants and all the boys -- to exit the Amish school before massacring the young girls. The one-room schoolhouse was subsequently torn down.
Jan. 17, 1989
Cleveland Elementary School
5 dead, all schoolchildren
Killer: Patrick Purdy (committed suicide)
Purdy is said to have fired more than 100 rounds in three minutes with an automatic rifle, prompting the state of California to ban assault weapons.
Nov. 12, 1966
Rose-Mar College of Beauty
5 killed: 4 women and a 3-year-old girl
Killer: Bob Smith
Smith ordered his victims to lie on the floor in a circle and then shot each of them in the head. A woman and a baby survived. Reports later emerged that he was a fan of mass murderers Richard Speck and Charles Whitman.
March 21, 2005
Red Lake Senior School
Red Lake Indian Reservation, MN
7 killed: 5 fellow students, 2 adults
Killer: Jeffrey Weise (committed suicide)
Weise, 16, shot and killed five schoolmates, a teacher and an unarmed guard before taking his own life. Weise had earlier killed his grandfather and his grandfather's companion.
April 2, 2012
Killer: One L. Goh
Goh, 43, a former nursing student at private Oikos University near the Oakland International Airport, sprayed gunfire on a classroom in one of the deadliest attacks ever on a California campus. He was arrested an hour later at a store.
Sources: Wikipedia, Reuters, ABC News, Fox News