The Washington Post has spent years tracking how many children have been exposed to gun violence during school hours since the Columbine High massacre in 1999. The federal government does not track school shootings, so The Post pieced together its numbers from news articles, open-source databases, law enforcement reports and calls to schools and police departments. While school shootings remain rare, there have been more in 2021 — 34 — than in any year since at least 1999, despite most students not attending school for the first two months of 2021. The count now stands at more than 292,000 children at 310 schools. The Post has found that at least 157 children, educators and other people have been killed in assaults, and another 356 have been injured. One dot (•) represents 10 children exposed to gun violence. The bigger the dot is, the more student expose to the gun shoot. Mouse over the dots, the graph will shows detile information regards the event. And also a line links to the timeline shows when it happens.