About 95% of American public schools conduct some form of regular active shooter safety drill — sometimes called a lockdown or active threat drill — according to the National Center for Education Statistics. But concerns are growing that these drills have not been proven effective in preventing violence and that they may even traumatize some students.

In a 2019 research paper, James H. Price and Jagdish Khubchandani found a lack of empirical evidence in favor of active shooter drills and other “hardening” measures used in schools. Partly this is because gun violence in school remains very rare.

And yet, the school security industry is worth a reported $3 billion. Guy Grace with the Partner Alliance for Safer Schools, an educator and industry partnership, insists that twice a year active shooter drills for students are an important piece of violence prevention.