K-12 School Security: A Guide for Preventing and Protecting Against Gun Violence (2nd Edition) [open pdf - 1MB]
"Educational agencies and institutions face a myriad of threats that include tornadoes, hurricanes, student bullying, drugs, and gang violence, just to name a few. School officials conduct assessments to properly prepare and mitigate these hazards on a continuous basis. This resource guide was developed to address only one of the specific threats that schools face - gun violence. The intent is to outline preventive and protective measures specifically for K-12 institutions to address the risk posed by an active shooter."
U.S. Department of Homeland Security: https://www.dhs.gov/