Statement of Purpose The US has experienced 48 active school shootings in the past twenty years. During this time, K-12 schools have undertaken efforts to modify their school environment in response to the anticipation of gun violence. However, it is unclear whether there is evidence that these strategies are effective.

Methods We identified the most common school tactics and policies that are being implemented in K-12 schools across the US: (1) target hardening (e.g. metal detectors, locked classroom doors, security cameras), (2) presence of zero tolerance policies, (3) presence of school resources officers (whether armed with lethal or non-lethal forces), (4) implementation of emergency preparedness programs (e.g. active shooter training drills and first-aid and hemorrhage control training programs), (5) behavioral threat assessment efforts, (6) policies that allow for teachers or administrators to be armed with firearms, and (7) notification technologies. We systematically reviewed the literature over the past two decades to determine i) which school environmental factors have evidence supporting their effectiveness at deterring gun violence and ii) where the gaps in the literature are.

Results Our work confirmed that while there is a large number of strategies available to schools, there is very limited empirical evidence as to their efficacy. Of the evidence that exists, a preliminary review of the literature indicates that behavioral threat assessment efforts may be effective and conversely, that certain hardening efforts such as metal detectors are not effective at deterring violence.

Conclusions Notably, K-12 schools are implementing several policies and practices intended to prevent gun violence that do not have an evidence-base.

Significance Our review also highlights the impact efforts may be having on child well-being and on school communities at-large. Implications for future research and for how school professionals might more effectively consider available information about these safety strategies will be discussed.