ATLANTA — The shooting of more than a dozen students at a Kentucky high school might have been expected to shock the nation, but Americans seem numbed by the apparent frequency of school shootings since 20 children and six adults were killed at a Connecticut elementary school in 2012, gun-control advocates say.

President Donald Trump took more than 24 hours to express sorrow about the shooting on Twitter — but tweeted about text messages between FBI agents and immigration in the meantime — while Canada’s prime minister, Justin Trudeau, tweeted condolences and called Kentucky’s governor the same day. Although the story led many newscasts, much coverage of the shooting in Benton, Kentucky, emphasized how students put past safety training into practice, running as far as a mile to escape the gunfire.

A 15-year-old boy was in police custody after authorities say he walked into Marshall County High School armed with a pistol Tuesday morning and immediately started firing. Two 15-year-old classmates were killed and 18 others were injured.

Gun safety and school safety advocates say the shock factor has disappeared amid years of school shootings, making them feel like common, everyday events.

“It is a story that feels probably like the movie `Groundhog Day,”’ said Shannon Watts, who founded Moms Demand Action after watching the shooting at a Newtown, Connecticut, elementary school that killed 20 children and six adults.

“It almost is like some kind of bar has been set (since Newtown), and if school shootings don’t reach that bar, then maybe they’re not newsworthy, which is in itself wrong,” Watts later added. “We have to care every time a gun goes off on school grounds, no matter what the reason is ... because we are the only developed nation where this happens.”

In the five years since the Sandy Hook Elementary School shooting, the United States has had 283 school shootings — 11 since just the beginning of this year — by gun control advocates’ count. The day before the shooting in Benton, a 16-year-old boy shot and injured a 15-year-old girl in the cafeteria at a high school in Italy, Texas — barely a blip on the national news.

Katherine Newman’s book “Rampage: The Social Roots of School Shootings,” zeroes in on two shootings, one of which occurred in Paducah, Kentucky, just 24 miles (40 kilometers) from Benton.

These types of school shootings — rampage shootings — remain uncommon, she said. However, because they are lumped in with all sorts of other shootings near or at schools, they feel like they’re happening more frequently.

For example, among the 11 cases this year some count as a school shooting was a 31-year-old man who killed himself in the parking lot of a Michigan elementary school. In researching the 2004 book, Newman said they tracked school shootings from 1970 to 2000 and identified 20 that fit the rampage category.