In the 2005–06 school year, 40 percent of American public schools drilled students on lockdown procedures in the event of a shooting; by the 2015–16 school year, 95 percent did.

Nolle K., Guerino P., and Dinkes R., “Crime, Violence, Discipline, and Safety in US Public Schools: Findings from the School Survey on Crime and Safety: 2005-06”. US Department of Education. (2007), https://bit.ly/36J5hSW. Musu-Gillette L., et al. “Indicators of School Crime and Safety: 2017”. National Center for Education Statistics, Institute of Education Sciences, and Bureau of Justice Statistics. (2018). https://bit.ly/316yqpS.