Seventeen high school students lay down for three minutes in front of the White House on Monday to represent the lives lost during the shooting at Florida’s Marjory Stoneman Douglas High School and the amount of time it takes to buy a gun.

They were joined by several hundred protesters who demanded that lawmakers act to end gun violence during an emotional demonstration on Presidents’ Day.

The D.C. protest echoed those orchestrated in Parkland, Fla., and beyond by teenagers who are emerging as powerful advocates for stronger gun control following one of the worst mass shootings at a school in U.S. history.

“This could be a breaking point,” said Whitney Bowen, 16, an organizer of the D.C. protest. “We’re still just 16, but at least we’re old enough to have our voices be heard.”

Bowen, a junior at the Potomac School in McLean, Va., was at school when she received a news alert about the shooting in Florida. She and her friends learned the details of the tragedy via social media. Then, inspired in part by listening to interviews with Douglas students on Twitter and Facebook, Bowen and her friend, Eleanor Nuechterlein, created a Facebook group, Teens for Gun Reform, and a Facebook event invitation to promote the “lie-in.” News of the event spread quickly online, with more than 700 people from around the region expressing interest.

“We’re not 18 yet so we can’t vote, but we have an advantage living in D.C. and as teenagers with access to social media,” Bowen said. “I don’t want to be known as a member of the mass shooting generation. It’s horrible and it’s devastating and it’s not the legacy I want to leave.”

The protesters — adults as well as students — were joined by a group of activists who have been demonstrating outside the White House every Monday since the 2012 shooting in Aurora, Colo., when 12 people were killed in a movie theater.

For two hours each week, members of the group talk with passersby about changes in gun laws, including instituting universal background checks and creating gun-free school zones.

Linda Finkel-Talvadkar, 66, an original member of the group, said the youths’ passion mirrors that of students in her generation who took to the streets demanding an end to the Vietnam War.

“That resulted in policy changes and a president not running again, so definitely these young people have the power to create the change we want to see,” she said. “They are our future, and our hope lies with them.”

After the three minutes had passed, scores of young people and adults joined the original 17 for the lie-in, resting with their arms crossed on the wet street outside the White House for nearly 20 minutes. Several parents wiped away tears as they watched.

Some students then turned in the direction of the White House, chanting, “Shame on you,” “Don’t be complacent” and “Hey, hey, NRA, how many kids have you killed today?” They carried American flags and signs, including one that read “Am I next?”

President Trump, who visited Parkland, Fla., last week, was playing golf on Monday in West Palm Beach, 40 miles from the site of the school shooting.

The White House said Monday that Trump, who met with members of the Parkland community, is open to congressional efforts to strengthen federal background checks for gun buyers. But Congress for years has not enacted even modest gun measures, and it is not clear that this effort will be different.

Jackson Baer, 17, who was among those chanting, said he thinks that the younger generation will be responsible for affecting change.

“I believe in the Second Amendment,” said Baer, a junior at Winston Churchill High School in Montgomery County, Md. “But change needs to happen. It won’t be easy, but we will make it happen.”

Nuechterlein, a junior at Potomac, said students are pushing for background checks before all gun sales, public and private, among other changes.

“Both Republicans and Democrats should believe we need to end school shootings,” she said. “At the end of the day this doesn’t come down to politics — it’s about trying to make sure fewer kids are scared when they are going to school.”

More than 150,000 students attending at least 170 primary or secondary schools have experienced a shooting on campus since the killings at Colorado’s Columbine High School in 1999, according to an ongoing Washington Post analysis.

For Elodie Camus, a sophomore at the British International School of Washington, mass shootings and the lack of government action that follows them have become almost routine.

“It’s so horrible that we keep watching this unfold, and that nothing much has been done to change it,” said Camus, 16, who was in elementary school in 2012 when a shooting rampage in Newtown, Conn., left more than two dozen people dead, most of them first-graders. “There is a constant threat of this happening because you can get these weapons so easily.”

A candlelight vigil at George Mason High School in Falls Church, Va. was planned for Monday night to remember the victims of the Douglas shooting. Seton McIlroy, a volunteer with the Virginia chapter of Moms Demand Action for Gun Sense in America, said the group planned the vigil after hearing an “outcry from local teenagers” who want to make their voices heard.

“Tonight is about those teenagers and allowing them to express their grief and frustration,” she said. “They’ve made it really clear they want to start leading.”