Large rallies with crowds estimated in the tens of thousands in some cases also unfolded in such cities as Boston; New York; Los Angeles; Chicago; Houston; Phoenix; Fort Worth, Texas; Minneapolis; and Parkland, Florida, the site of the February 14 attack at Marjory Stoneman Douglas High School that left 17 people dead.
Students chanted "enough is enough" and held up signs with slogans like "our ballots will stop bullets" at a rally in Parkland, Florida, where 17 people were killed in a school shooting last month.
The St. Louis march will start at 10 a.m.at Aloe Plaza, which is right across from Union Station, and circle back to the plaza for speeches organizers say the public is invited to attend. In a coordinated school walkout on March 14, thousands of students left their classrooms for 17 minutes to remember the 17 victims of the Parkland shooting.
Washington is generally nonchalant about protests, but Saturday's gathering has prompted more attention and speculation than usual.
"It's pretty simple for me", said Zoe Tate, 11, from Gaithersburg Middle School in Maryland, explaining why she marched in Washington.
The Washington rally is among more than 800 events scheduled worldwide, with US demonstrations set from San Clemente, California, to NY and Parkland, according to gun-control group Everytown For Gun Safety.
"The point is to be here, but after being here, to stay active", she said. The organization defines mass shootings as four or more shot or killed, not including the shooter.
Isabel Bousson, a Lincoln East High School junior and a member of the board of organizers for the march in Lincoln, said she sees school safety as an "everybody issue" that should involve both sides of the political aisle.
"I know Trump would do it", Clark said, praising the Republican president. Those devices allow semi-automatic weapons to fire like machine guns. "We are the ones that are going to be dealing with the ramifications of everything that happens today in the future".
More than 800 marches are planned in cities across America and dozens of locations overseas to be held at roughly the same time.
"The media focus on school shootings can oftentimes be biased towards white, privileged students".
They predict a half-million demonstrators Saturday near the U.S. Capitol building for a several-hour rally.
The poll by The Associated Press and NORC Center for Public Affairs Research said the support for gun control is up from 61 percent in October 2016 and up from 55 percent since the poll first asked the question in October 2013.
"I think the kids are doing awesome", said Iris Diaz, 44, the mother of a Stoneman Douglas senior and alumnus of the school, who traveled to Washington for the march. One way they hope to do that is by registering young voters and channeling energy into the midterm elections.