A gun is fired on a school campus in America nearly twice a week. Suicide, homicides, a police shooting, attacks on students by other students: more than once a month this past year, gunfire on American school and university campuses has turned deadly, according to a database of school gunfire incidents compiled by advocates.

In the latest in a series of brutal shootings in California, and 11-year-old boy and a 16-year-old boy were shot to death in the parking lot of an elementary school in Union City, California, in the early hours of Saturday morning. Police had no immediate motive for the shooting, but said that a suspect or suspects had fired into the van the boys were sitting in multiple times.

Schools are one of the safest places for kids in the United States, and shootings in and around schools represent only a tiny fraction of the violence that children face here on a daily basis. But even the small amount of gun violence that occurs at American schools adds up.

Since the Columbine shooting in 1999, at least 233,000 kids across 243 schools have been exposed to gun violence during school hours, a Washington Post investigation found.

Experts are quick to put that number in context. Researchers found that nearly 1,300 American children aged 17 and younger die from gunshot wounds each year, and they are more likely to be killed in homes or neighborhoods than at school.

Domestic violence is particularly deadly. In San Diego, a domestic violence mass shooting claimed the lives of three young boys and their mother, all shot to death by the boys’ father on 16 November, according to police. The fourth brother, nine-year-old Ezekiel Valdivia, died on Saturday afternoon, the San Diego Union-Tribune reported.

That single domestic violence shooting was deadlier than any of the school shooting attacks in the United States so far in 2019, according to tallies compiled by the Washington Post and the New York Times.

“Gunfire on school grounds is just the tip of the iceberg when it comes to how gun violence affects children and teenagers,” said Ruhi Bengali, a senior associate at Everytown for Gun Safety, the country’s largest gun control advocacy organization.

But tracking gun violence on school grounds, as Everytown has done since after the 2012 Sandy Hook elementary school shooting, does provide a window into the many ways gun violence burdens young people, even in places that are “inherently meant to be safe spaces for learning”, Bengali said.

Everytown’s analysis found that 20% of all gunfire on school grounds comes from unintentional shootings, but that even these “actually resulted in a fair number of injuries. Gun suicides, with no intent to harm anyone else, represented 12% of all incidents,” she said.

As with other kinds of gun violence in America, students of color, and black students in particular, were disproportionately affected.

Black students make up only 15% of the school population for K-12 schools, yet represented 24% of student victims in instances of gunfire on school grounds, she said.

For the students affected by ongoing gun violence in and around their schools, local officials can offer additional counselors, but little evidence of national change on gun laws: Republican lawmakers have blocked any substantive gun control laws for the past quarter-century.

In Union City, where the two kids were killed in the elementary school parking lot, students are out of school this week for the Thanksgiving holiday, but will have “district and community mental health providers available” when they return to school, spokesman John Mattos said.

Not far away, students at Carl Munck elementary school in Oakland have also had additional counselors available to them. The president of the school’s Parent Teacher Association, Misty Smith Walton, was shot to death outside her Oakland apartment earlier this month.

Her death wasn’t a school shooting. But that didn’t mean it does not affect the school.

“She was always looking to improve her sons’ classes and their school, always there to do whatever was needed in the front office, on the yard or anywhere else on campus,” the superintendent said in a statement, calling her death a “horrific crime”.