Saturday marks the 20th anniversary of the Columbine High School shooting, which left one teacher and 14 students, including the two perpetrators, dead. Since then, according to The Washington Post, there have been 237 school shootings in the U.S., resulting in 403 killed or injured. But we don’t know the exact numbers.

School shootings are a public-health problem because they affect the health and well-being of communities and individuals. As epidemiologists, we investigate the patterns and determinants of disease and injury. We start by counting. In the U.S., we have comprehensive registries that enumerate cancer cases. We keep detailed track of motor vehicle injuries and fatalities. Why don’t we know the exact tally of how many school shootings there have been in the past 20 years?

To start, there is a lack of agreement on what counts as a “school shooting.” Does it have to be during school hours? Do college campuses count? What if a student brings a gun to school but it’s never discharged? For instance, the Center for Homeland Defense and Security counts 730 firearm-related incidents at K-12 schools in the 20 years since Columbine, killing or injuring 1,025 people. To put that in perspective, about 7,000 children are killed or injured with firearms in the U.S. each year.

School mass shootings are especially unique in their intensely devastating impact to communities. School shootings as a whole are happening more frequently: in 2018 there were 25 school shootings, more than ever before recorded in one year, and so far 2019 is on track to match or exceed this sobering record.

The relatively small number and lack of standardized data collection greatly limit our ability to evaluate all aspects of school shootings with robust epidemiologic methods. But over the past 20 years, we have identified some nodes where policymakers and school administrators can mitigate the severity of a school shooting and reduce the likelihood of one occurring in the first place.

After Columbine, and each subsequent highly publicized school shooting in the U.S., schools have focused on methods to “harden” themselves as targets through increased security measures: surveillance cameras, metal detectors, and positioning armed police officers on campus, known as school resources officers. Since 2000, the U.S. government has distributed nearly $1 billion to schools across the country to fund school resource officers. But accumulating research has shown that the conspicuous security, including the presence of school resource officers, have little to no effect in preventing school shootings, or reducing casualties.


The use of long guns such as semi-automatic rifles is strongly associated with increased victim counts, even though they are used in a minority (fewer than 15 percent) of school shootings overall. Policies limiting access to such firearms by people who are at high risk of harming themselves or others may reduce casualties in school shootings. In school mass shootings, one of the most common motives is retaliation for bullying. This is also a promising avenue for prevention. Measures such as anti-bullying programs and policies to make school a more inclusive environment appear to be effective in preventing school violence and shootings.

Instead of reactively implementing conspicuous security measures to make themselves “hard” targets, schools should adopt “soft” measures to maintain a positive, inclusive environment, prevent bullying, and enhance access to mental-health resources. Of course physical or building security measures should not be ignored, but improving school climate and reducing firearm access by people at high risk of perpetrating violence are far more likely to be effective deterrents and reduce casualties.

School shootings affect entire communities and violate the sanctity of our schools. Epidemiologists have an important role in addressing school shootings, but we need better data on firearm injuries. The limited data we do have demonstrate that a public-health approach to school shootings should recognize their complexity and employ a multipronged approach.

Preventing school shootings is not just the responsibility of school administrators. We all have a role to play to protect our youth and school staff, through deterring easy access to firearms by those who have posed harm to others, and checking in on each other and our communities.