Thousands of students walked out of classes across the United States on Friday, marking the 19th anniversary of the massacre at Columbine High School with a show of unity aimed at pressuring politicians to enact tighter gun restrictions.

Students from more than 2,600 schools and institutions were expected to leave their classes at 10:00 a.m. local time, organizers said. Many wore orange, a color that has come to represent the movement against gun violence, as they observed a 13-second silence in honor of those killed at Columbine.

On April 20, 1999, two Columbine seniors rampaged through their school, killing 12 of their classmates and a teacher before committing suicide. Since then, mass shootings have occurred with shocking frequency across the United States.

The second deadliest public school shooting in U.S. history took place in Parkland, Florida, on Feb. 14, leaving 17 dead. The shooting set off a national student movement calling for an end to gun violence and tighter gun restrictions. (Reuters)

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