The attack on a Texas elementary school on Tuesday was the deadliest school shooting since 2013 when a leading gun control advocacy group began tracking such shootings.
Nineteen children and two teachers were killed in Uvalde, Texas, according to Gov Greg Abbott. The gunman also died.
Everytown for Gun Safety started following school shootings in 2013 "to gain a better understanding of how often children and teens are affected by gun violence at their schools and colleges, and in response to a lack of research and data on the issue," according to a statement on its website.
The effort was initiated in the year following the massacre at Sandy Hook Elementary School in Newtown, Connecticut. In December 2012, 20 children and six adults were killed at the school.
The shooting in Parkland, Florida, at Marjory Stoneman Douglas High School, where 17 were killed, was the second deadliest school shooting since Sandy Hook.