NEW YORK
BRENDAN MCDERMID/REUTERS
Thousands participate in the National School Walkout to protest gun violence on April 20 in Washington Square Park. The youth-led demonstration was one of more than 2,500 nationwide on the 19th anniversary of the Columbine High School massacre, and the second of its kind in two months. A 17-minute rally on March 14 honored the 17 killed in Parkland, Florida, in February.