Thousands of students have again walked out of classes across the US on the 19th anniversary of the massacre at Columbine High School.
It's a show of unity aimed at pressuring politicians to enact tighter gun restrictions.
Students from more than 2600 schools and institutions planned to leave their classes at 10am local time on Friday, organisers said.
It was the second student walkout since the February 14 massacre of 17 people at Marjory Stoneman Douglas High School in Parkland, Florida, and the emergence of a national student movement to end gun violence and tighten gun restrictions.
Many of the demonstrators wore orange, a colour that has come to represent the movement against gun violence, as they observed a 13-second silence in honour of those killed at Columbine.
"I'm trying to get an education, but I still have a small fear that someone will come in with a gun," said Ayanna Rhodes, 14, who walked out of Washington International School to join hundreds of local students in front of the US Capitol. "It's an issue that's been in this country for a long time."
Two gunman went on a shooting rampage at the Colorado high school in 1999, leaving 12 students and a teacher dead before killing themselves. The massacre stunned the nation but since then, school shootings have become commonplace.
Even as students prepared for their protest on Friday morning, news began trickling out that one person was wounded in a shooting at a high school near Ocala, Florida.
The latest gun violence unfolded about 360km northwest of the Parkland high school, where two months ago a former student killed 17 people in the deadliest high school shooting in US history.
Despite widespread revulsion over the school shootings, the issue of gun control remains sensitive in Colorado and across the country, where the Second Amendment of the US Constitution guarantees the right to bear arms.
Dudley Brown, president of the Colorado-based National Association for Gun Rights, said the gun-control movement seeks to have the government take away constitutional rights.
"The main objective of these students is to ban firearms completely, and confiscate the firearms of law-abiding Americans," Mr Brown said. "We will oppose them at every step."
Students walked out of high schools in New York, Detroit and Washington, among hundreds of other cities and towns. Many were waving placards with slogans such as "No more gun violence" and "I should be worried about grades, not guns".
Outside the White House, scores of young protesters sat in silence while they listened to the names of gun violence victims read aloud.
The walkouts, speeches and drive to sign up voters were aimed at pressuring US politicians to enact more restrictions on gun sales in the run-up to November's midterm congressional elections.
After walking out of class and observing the 13-second silence, students were free to decide how to demonstrate. National organisers suggested marches to the offices of local lawmakers, speeches, and voter registration activities.
On the evening before the national walkout, Colorado gun control activists rallied near Columbine High School, calling for an end to gun violence.