This Chart Shows the Number of School Shooting Victims Since Sandy Hook

The nation is still reeling from a shooting at a Parkland, Fla. high school last week that left 14 students and 3 teachers dead and injured more than a dozen others. It is the worst school shooting since the Dec. 14, 2012 massacre at Sandy Hook Elementary School that claimed the lives of 20 children and 6 adults.

While school shootings appear to be dramatically on the rise, tallying the toll of these tragedies runs into the same problem as counting victims in mass shootings: What constitutes a school shooting? Since government data typically lags by years and is often fraught with errors, the task of tracking such incidents as they occur falls to third-party groups. In this case, most media outlets rely on either EveryTown.org, a gun control advocacy group backed by Michael Bloomberg that tracks such incidents, or the Gun Violence Archive, an independent effort organized by volunteers to track gun violence in the U.S.

According to EveryTown, there have been 17 school shootings in 2018 alone, and 290 since 2013, shortly after Sandy Hook. These incidents range from mass shootings like last week’s in Florida to accidental discharges of firearms, after-hours fights between adults in a school parking lot and suicides.

TIME examined the reports on the 86 attacks in EveryTown’s data since 2013 that are categorized as “Attack on other persons(s) resulting in injury or death,” not including those that occurred on college campuses. We considered a school shooting to meet the following definition:

Of those 86 incidents, we found that 63 met this definition. The remaining 23 mainly involved gunfire exchanged at night in a school parking lot between people who were not affiliated with the school. Here is the complete list of those 63 school shootings, starting with Sandy Hook, ordered by the number of people killed.

A large number of the school shootings from the past several years resulted in one non-fatal injury. This does not diminish the extreme danger that a gun on a school campus represents — a low injury or death toll can often be credited to a fast, organized response from teachers and administrators to lock down the school.

Of the 17 school shootings in 2018 that EveryTown registers, 4 meet the above definition, including the Parkland massacre as well as a Jan. 23 shooting in Benton, Ky. that killed two students and wounded 14. (Several others were wounded in the aftermath.) The remaining 13 from this year either did not result in any casualties or were the result of an accidental discharge.

All told, since 2013 we counted 6 adults and 35 children killed in these types of school shootings, as well as 12 adults and 92 children injured.

This count contrasts sharply with a New York Times analysis of the Gun Violence Archive, which tallied 239 school shootings since 2014, including those on college campuses, resulting in 138 deaths. The Times does not published information on individual incidents for comparison to EveryTown, but does not appear to be limited only to cases of malicious intent.

If school shootings of any variety are going to be seriously addressed, it is important to parse the different reasons that these incidents occurred, and what if anything motivated the shooter. Clearer data would be a good first step.