FILE - Lillie Perez, 11, holds a sign during a "March for Our Lives" protest for gun legislation and school safety March 24, 2018, in Houston. Students and activists across the country planned events Saturday in conjunction with a Washington march spearheaded by teens from Marjory Stoneman Douglas High School in Parkland, Fla., where over a dozen people were killed in February. There have been dozens of shootings and other attacks in U.S. schools and colleges over the years, but until the massacre at Colorado's Columbine High School in 1999, the number of dead tended to be in the single digits. (AP Photo/David J. Phillip, File)