The shootings at Sandy Hook Elementary School in Connecticut are the latest in the United States’ long history of massacres at schools and colleges.
The worst was the 2007 Virginia Tech massacre when gunman Seung-Hui Cho killed 32 people and wounded 25 others before killing himself.
Four years later Radford University student Ross Truett Ashley, 22, shot and killed a police officer on the campus of Virginia Tech, before killing himself.
Although the notorious “Batman” shootings in Aurora, Colorado, did not take place on a campus, James Holmes, the alleged killer, was a student at the University of Colorado Denver.
The 24-year-old is charged with 24 counts of murder and 116 counts of attempted murder after the cinema shootings in June which left 12 people dead and 58 wounded.
The trend of school and university killings stretches back decades. In 1966, 16 people were killed and more than 30 wounded during a 96-minute rifle rampage by student Charles Whitman at the University of Texas in Austin.
In 1970, four students were killed and nine wounded by National Guard troops dealing with anti-war protests on the campus of Kent State University in Ohio.
In 1991, Gang Lu, a graduate student in physics from China, apparently upset because he was passed over for an academic honour, opened fire in two buildings on the University of Iowa campus.
Five people were killed before the 28-year-old turned his weapon on himself.
In 1996, San Diego State University graduate engineering student Frederick Martin Davidson, 36, was defending his thesis before a faculty committee when he produced a handgun and killed three professors.
In 1999, 12 students and a teacher were murdered at Columbine High School in Colorado by two boys who then killed themselves.
And in an apparent murder-suicide in 2000, James Easton Kelly, 36, a University of Arkansas graduate student who had been dropped from a doctoral programme, and John Locke, 67, the professor overseeing his coursework, were shot dead.
In 2002, failing University of Arizona nursing student Robert Flores, 40, killed a female instructor in her office.
Minutes later, armed with five guns, the Gulf War veteran entered one of his nursing classrooms and killed two more instructors before killing himself.
The same year saw graduate student Peter Odighizuwa, 42, return to Virginia’s Appalachian School of Law, from which he had been dismissed, and kill the dean, a professor and a student before being tackled by students.
And in April this year, seven people were shot dead and three injured in shootings at the Christian Oikos University in California.
One Goh, a former nursing student at the Oakland institution, is accused of carrying out the murders, allegedly after being teased about his poor English skills.