The nation’s two largest education unions and a gun-control nonprofit are recommending that schools stop holding active-shooter drills.

The groups say they’re concerned that such drills traumatize students and staff and could hinder children’s academic performance.

School-shooter drills are routine across the United States: about 95% of public school districts regularly hold active shooter drills, NPR reported. Some states require schools to do so.

But there’s little evidence that these drills help prevent deaths during active shootings, according to a white paper released Tuesday by the American Federation of Teachers and the National Education Association. Everytown for Gun Safety (Everytown), an anti-gun advocacy organization financed by democratic presidential candidate and former New York City Mayor Michael Bloomberg, joined the unions in releasing the report.

Instead, the organizations argue, these lockdowns may contribute to students’ anxiety, cause sleeplessness or drum up fear or past trauma.

“Mental health professionals have begun warning about the effect of these drills on students’ well-being and about the possible short- and long-term consequences on school performance and physical and mental health,” the organizations wrote. The white paper does not include research on active-shooter drills or their effectiveness, but the National Association of School Psychologists and the National Association of School Resource Officers said in 2014 that these drills can cause harm if they aren’t “conducted appropriately.”

Everytown and the education unions suggest that schools train staff — but not students — on how to evacuate their class or offer emergency medical assistance if an active shooter enters a school.

If schools choose to drill students, the organizations recommend that schools announce the lockdown in advance to staff, students and parents. Some school districts, such as Henrico County Public Schools in Virginia, have already taken such steps, The Associated Press reported. The white paper also cautions against using simulations that mimic an actual school shooting.