Thousands of students across the US will mark the 19th anniversary of the massacre at Columbine High School by walking out of classes, in a show of unity intended to put pressure on politicians to enact tighter gun restrictions.
Students from more than 2600 schools and institutions are expected to walk out of class at 10am local time on Friday, organisers say.
They have been asked to wear orange, the official colour of the campaign against gun violence, and observe a 13-second silence to honour the victims killed at Columbine.
"This movement is here to stay. No more excuses. We want solutions," organisers said on Thursday on Facebook.
On April 20, 1999 two Columbine seniors killed 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 US history occurred in Parkland, Florida, on February 14, leaving 17 dead. The shooting set off a national student movement calling for an end to gun violence and tighter gun restrictions.
Friday's walkouts and drive to sign up voters are aimed at pressuring US politicians to enact tighter restrictions on gun sales in the run-up to November's mid-term congressional elections.
On Thursday, Colorado gun control activists rallied near Columbine High School, calling for an end to gun violence.
Columbine has not held classes on April 20 since the massacre, a district spokeswoman said, so there would be no walkout at the school. Students were encouraged to take part in community service.
The latest national rally comes more than a month after tens of thousands of students from some 3000 schools participated in the #ENOUGH National School Walkout to demand that lawmakers seek tighter gun control regulations.
It also follows "March For Our Lives" rallies in cities across the United States on March 24 that were some of the biggest US youth demonstrations in decades, with hundreds of thousands of young Americans and their supporters taking to the streets to demand tighter gun laws.
Dudley Brown, president of the Colorado-based National Association for Gun Rights, said the gun-control movement seeks to have the government take away rights.
"The main objective of these students is to ban firearms completely, and confiscate the firearms of law-abiding Americans," Brown said. "We will oppose them at every step."
