The BBC News website charts the history of gun violence in US schools.
October 2007: A teenage gunman reportedly shoots and wounds five people at a high school in Cleveland, Ohio, before killing himself.
April 2007: At least 32 people are killed in two shooting incidents in the campus of Virginia Tech university in Virginia.
October 2006: A 32-year-old gunman shoots dead at least five girls at an Amish school in Pennsylvania, before killing himself
September 2006: Gunman in Colorado shoots and fatally wounds a teenage schoolgirl, then kills himself; two days later a teenager kills the headteacher of a school in Cazenovia, Wisconsin
November 2005: Student in Tennessee shoots dead an assistant principal and wounds two other administrators
March 2005: Minnesota schoolboy kills nine, then shoots himself
May 2004: Four people injured in shooting at a school in Maryland
April 2003: Teenager shoots dead head-teacher at a Pennsylvania school, then kills himself
March 2001: Pupil opens fire at a school in California, killing two students
February 2000: Six-year-old girl shot dead by classmate in Michigan
November 1999: Thirteen-year-old girl shot dead by a classmate in New Mexico
May 1999: Student injures six pupils in shoot-out in Georgia
April 1999: Two teenagers shoot dead 12 students and a teacher before killing themselves at Columbine School in Colorado
June 1998: Two adults hurt in shooting by teenage student at high school in Virginia
May 1998: Fifteen-year-old boy shoots himself in the head after taking a girl hostage
May 1998: Fifteen-year-old shoots dead two students in school cafeteria in Oregon
April 1998: Fourteen-year-old shoots dead a teacher and wounds two students in Pennsylvania
March 1998: Two boys, 11 and 13, kill four girls and a teacher in Arkansas
December 1997: Fourteen-year-old boy kills three students in Kentucky
October 1997: Sixteen-year-old boy stabs mother, then shoots dead two students at school in Mississippi, injuring several others