Across the country this year, according to media reports, at least 11 shootings have taken place on U.S. high school or college campuses, including the attack in Santa Clarita, California, today. And school officials and law enforcement agencies have responded to dozens more credible threats of attacks.

The shootings have occurred inside gyms and classrooms, in parking lots and hallways, and in the crowd at a high school football game.

The New York Times defined a school shooting as one that occurred on campus, in which students were shot, or the suspected perpetrator was a student, or both.

Jan. 31: Memphis, Tenn.

A 14-year-old at Manassas High School was shot with a pellet gun at school, according to news reports. The student’s injury was not life-threatening.

Feb. 8: Baltimore

A man entered Frederick Douglass High School and shot and injured a staff member, prompting students to hide in their classrooms at the sound of gunfire. The police said they believed that the gunman had targeted the victim, a 56-year-old special education assistant.

Feb. 12: Kansas City, Mo.

A teenage girl was shot and killed outside a high school after an argument at an evening basketball game. Police said that the assailant and girl knew each other, and that it appeared the suspect had waited in the parking lot for her.

Feb. 26: Montgomery, Ala.

A 17-year-old student at Robert E. Lee High School was shot and wounded in an arm by another student, police said. The school was placed on lockdown and the assailant was arrested. According to news media reports, it was the second time in two years that a student had taken a gun to that school and shot another student.

Apr. 1: Prescott, Ark.

A 14-year-old eighth grader at Prescott High School was shot and injured by a classmate, who authorities said took a concealed handgun to school.

Apr. 30: Charlotte, N.C.

Two students were killed and four others were wounded after a gunman opened fire in an anthropology class at the University of North Carolina at Charlotte. One of the students who was killed, Riley Howell, was credited with charging and body-slamming the gunman, stopping the massacre.

May 7: Highlands Ranch, Colo.

One student was killed and eight others were injured in an attack on an English class at STEM School Highlands Ranch. Two students were apprehended and charged with the shooting, which took place near Columbine High School, the site of a massacre 20 years ago.

May 7: Savannah, Ga.

A Savannah State University student was shot and wounded in a residential hall on campus. Authorities said a man who was not a student was arrested in the shooting.

Aug. 30: Mobile, Ala.

Nine people between the ages of 15 and 18 were wounded when gunfire broke out at a high school football game. The police arrested and charged a 17-year-old student in the shooting, and later sought a second assailant when they found evidence of shots fired by a different gun.

Oct. 24: Santa Rosa, Calif.

A 17-year-old gunman shot a schoolmate twice just outside Ridgway High School and then walked calmly in to class, where his teacher did not realize anything was amiss, police said. The victim survived.

Nov. 14: Santa Clarita, Calif.

A 16-year-old pulled a handgun from his backpack at a high school in Santa Clarita, California, this morning and shot five students, killing two, authorities said. The gunman was in grave condition after shooting himself in the head, they said.