If in recent years it seems that school shootings are happening more frequently, occupying public discourse and media coverage, it’s because they are. Although school shootings are still very rare compared to daily gun violence, the data show they are happening more often.

It can be hard to measure school shootings without a clear definition of what exactly qualifies as a school shooting. This is why we sometimes see inconsistencies among publications when it comes to the number of school shootings each year.

For our purposes, we’re defining a school shooting as an incident in which there is an active shooter on school property, using the FBI’s definition of “active shooter”.

The FBI defines an active shooter as: “An individual (or individuals) actively engaged in killing or attempting to kill people in a populated area,” no matter the number of victims. The FBI excludes drug or gang violence and “accidental discharges of a gun.” In our definition, we also exclude incidents typically defined as domestic violence.

Using the Guns & America definition, we turned to the CHDS – K-12 School Shooting Database, maintained by the Center for Homeland Defense and Security, which gathers “each and every instance a gun is brandished, is fired, or a bullet hits school property for any reason, regardless of the number of victims, time of day, or day of week.”

Guns & America analyzed data from the CHDS – K-12 School Shooting Database, April 1999 through May 2019, filtering out situations that did not fit our definition of school shooting explained above.

You can read more about the methodology here.

20 Years, 68 School Shootings

Since 1999 — when the Columbine High School massacre occurred — there have been 68 school shootings.

In recent years, the average number of days between school shootings has been decreasing.

From 1999 to 2014, the average number of days between shootings was 124 days. From 2015 to 2018, the average was 77 days.

In the 13 years between 1999 and 2012, there were four periods of time longer than 400 days without a single school shooting. The longest period was one year and six months — or 574 days — from April 2001 to November 2002.

Then, on Dec. 14, 2012, 27 people were killed at Sandy Hook Elementary School in Newtown, Connecticut. Since Sandy Hook, the United States has not gone more than 231 days without a school shooting.

Credit Luis Melgar / Guns & America / Guns & America The average number of days between school shootings in the United States between 2015 and 2018 was 77 days.

The average number of days between school shootings in the United States from 2015 and 2018 was 77 days.

In 2018, there were nine school shootings, the highest number in the 20-year period since 1999. This year tied with 2012 as one of the two deadliest years: 30 people were killed and 52 were injured in those nine shootings. In 2012, 29 people were killed in school shootings and six were injured.

Credit Luis Melgar / Guns & America / Guns & America

Guns & America’s analysis of the the CHDS – K-12 School Shooting Database included filtering out incidents that occurred outside the school perimeter and those that didn’t happen during school days or during some other activity like sporting events.

The 68 school shootings were found among 486 incidents of firearms at schools within the 20-year period.

Methodology

Guns & America used data from the CHDS – K-12 School Shooting Database, produced and maintained by the Center for Homeland Defense and Security. This database collects “each and every instance a gun is brandished, is fired, or a bullet hits school property for any reason, regardless of the number of victims, time of day, or day of week.”

The original database collects records from 1970 to the present.

In the analysis, all firearm incidents occurring outside the school perimeter, as well as those that didn’t occur during school days or during other organized activity in the school (for example: concerts, plays, sporting events), were filtered out.

The Center for Homeland Defense and Security database research ranked every event from 1 to 5, with 1 being less reliable and 5 more reliable. Guns & America discarded firearm incidents that were defined as 1: “Independent Single Author/Moderator Blog, report/list lacking citations, or cited source cannot be located (e.g., newspaper headline title and story does not appear in searches),” as defined by the researchers.

Guns & America also excluded from shooting fatality counts any perpetrator who was killed or died by other means during the event. Victims who were killed in a location other than a school, but on the same day, by the same perpetrator, were also excluded.

Ex: In the case of the 2012 shooting at Sandy Hook Elementary School in Newtown, Connecticut, 26 victims are listed, excluding the perpetrator and his mother, who was killed at her home.

The dataset was revised to identify what cases fell into the definition of school shooting used by Guns & America as explained above. As a consequence, some of the incidents were categorized differently than they were in the original dataset. Cases that fell outside of the Guns & America definition of school shootings were discarded.

Other sources: FBI active shooter reports (2000-2013, 2014-2015, 2016-2017, 2018); The Washington Post school shootings database; RAND Corporation.

You can explore the full dataset used by Guns & America here.

Emily Alfin Johnson, Lisa Dunn, Francesca Piemonte Slesinger contributed to this reporting.

Guns & America is a public media reporting project on the role of guns in American life.