A day after the school massacre in Texas, Ohio teacher Renee Coley thought her sixth grade students would need time to process, so she opened class with a video about the news and started a discussion. Some students said they were sad. Some were dismayed the 19 slain children were so young.

After a few minutes, though, the conversation fizzled. Students were ready to move on with their day. To Coley, it was a grim reminder that the students had seen it all before, had grown accustomed to the ever-present threat of guns in school.

“They have no questions because these kids have grown up their entire lives and this has been the reality for them,” said Coley, who teaches in Reynoldsburg, outside Columbus. “They’ve processed this so many times . ... It’s just another news day for them.”

The interaction highlights how students across America have grown up numb to the violence that has been playing out throughout their lives in schools and communities — and in much greater frequency since the pandemic.

The bloodbath at Robb Elementary in Uvalde, Texas, Tuesday marked the deadliest school shooting in the

U.S. since the 2012 massacre at Sandy Hook Elementary in Newtown, Conn. Police say the shooter, an 18-year-old man, was killed by law enforcement at the school. Two teachers were also killed.

Although mass shootings of that magnitude are rare, researchers at the Naval Postgraduate School have recorded 504 cases of gun violence at elementary, middle and high schools since the start of 2020 — a number that eclipses the previous eight years combined.

The database includes a range of cases, including students brandishing guns or opening fire in classrooms, bathrooms, cafeterias or gyms. It counts students who have used guns to take their own lives at school. And it also tracks violence that

doesn’t involve students, including overnight shootings near school grounds.

An alarming number have involved teens who turned to violence to resolve spurof-the-moment conflicts, said David Riedman, a criminologist who co-founded the database at the Naval Postgraduate School’s Center for Homeland Defense and Security.

“The majority of those incidents are escalations of disputes,” Riedman said. “There are more teenagers carrying concealed handguns in school who are getting into fights and shooting people. And that is not something that we were seeing before the pandemic.”

Violence and other trauma have become common enough for schoolchildren that Chicago Public Schools developed a 15-page guide called “The Day After,” to help teachers and staff coach students through processing painful events.

The proliferation of guns in homes, coupled with an overburdened mental health system that has left many students without the help they need, has fueled the increase in school gun violence, researchers say.

In fact, violent incidents involving guns have increased across all of America since the pandemic started — not just in schools.

“Gun violence is like a flood, and when your community is flooded, all your buildings take on water,” said Dewey Cornell, a psychologist and director of the Virginia Youth Violence Project at the University of Virginia.