Active shooter drills, often also called “lockdown drills,” have become ubiquitous in American public schools since the 1999 Columbine massacre and the 2012 killings at Sandy Hook Elementary. Now most schools in the U.S. conduct training on how to handle such emergencies and save as many lives as possible despite ongoing questions about their effectiveness and the fact that school shootings account for less than 2% of all youth homicides.

According to the Department of Education, about 96% of schools conduct lockdown drills and 92% of schools have procedures in place for an active shooter situation. At least 40 states mandate these drills, pro-gun control group Everytown says, but with no federal standard for how these drills should be run, each state varies in approaches and standards.

Some school districts prepare their personnel for drills ahead of time, some tell staff and students as a drill is occurring, and others launch their drills with no warning at all, Reuters reported.

And the tactics used in drills also vary, with some using actors dressed as gunmen, teachers lined up and shot with an airsoft gun, and young students told to run and hide in small spaces for long periods of time. There have even been drills with simulated gunfire and fake blood, according to Vox. A major factor in determining how a drill plays out depends on which private company a district has contracted with to run the drills, like the nation’s largest for-profit active shooter preparedness provider ALICE Training Institute, which reportedly has trained more than 5,000 districts.

Everytown revealed in a 2020 report that active shooter drills traumatize students while not showing evidence of saving lives. The group now wants schools to get away from unannounced drills and events that mimic actual gun violence, Reuters said.

“What these drills can really do is potentially trigger either past trauma or trigger such a significant physiological reaction that it actually ends up scaring the individuals instead of better preparing them,” Melissa Reeves, former president of the National Association of School Psychologists, stated in the report.