Seventeen people are confirmed dead in Wednesday's shooting at Marjory Stoneman Douglas High School in Parkland, located in south Florida.
It marked the sixth school shooting incident in the U.S. since Jan. 1 that has either left students wounded or killed, according to the advocacy website Everytown for Gun Safety, which has logged or counted 290 school shootings since 2013.
There have been 18 overall school-related shootings this year, but most of those didn't lead to mass injuries or deaths, and in some cases involved bullets fired elsewhere striking school property.
The most recent school mass shooting happened at Marshall County High School in Kentucky, Jan. 23, when a 15-year-old student opened fire, killing two and injuring 17 others.
Other prominent school shootings in the United States:
• December 2012: Adam Lanza, 20, gunned down 20 children and six adults at Sandy Hook Elementary School in Newtown, Conn., before killing himself.
• February 2008: Shooter Steven Kazmierczak, 27, enters a lecture hall at Northern Illinois University, and kills five students and wounds 18 others before taking his own life.
• April 2007: Seung Hui Cho, a 23-year-old student, went on a shooting spree at Virginia Tech in Blacksburg, Va., killing 32 people, before killing himself. It was the deadliest school shooting in U.S. history.
• October 2006: Milk truck driver Charles C. Roberts, 32, enters a one-room Amish schoolhouse in Nickel Mines, Pa., and isolates the female students in the classroom before methodically executing them. He kills five girls and wounds several more. Roberts then commits suicide.
• March 2005: Sixteen-year-old Jeff Weise killed his grandfather and a companion of his grandfather's, then headed to a high school on the Red Lake Indian Reservation in Minnesota. He killed five students, a teacher and a security guard before taking his own life.
• April 1999: Students Eric Harris, 18, and Dylan Klebold, 17, opened fire at Columbine High School in Littleton, Colo. They killed 12 students and one teacher and wounded more than 20 others before killing themselves in the school's library.
• August 1966: Charles Joseph Whitman, a former U.S. Marine, shot and killed 16 people from a university tower at the University of Texas in Austin before being shot by police.
The deadliest school massacre in U.S. history didn't involve guns.
On May 18, 1927, a bomb destroyed the Bath Consolidated School in Bath, Michigan. Forty-four people, including 38 students, were killed. The bomb was planted by a local school board member.