About 1,000 people, including a group of students from Florida's Marjory Stoneman Douglas High School, gathered in a park near Columbine High School to push for gun control and to highlight the importance of voting in the next election.
The group gathered Thursday evening, the day before the 19th anniversary of the Colorado school shooting that killed 12 students and a teacher.
Some held signs that read, "Change Gun Laws," ''Change Congress" and "I Will Vote."
Students at high schools across the country are expected to walk out of classes Friday to call for gun control. Columbine High School will be closed, and students there will stick with their tradition of holding a day of service to commemorate the tragedy.
By COLLIN BINKLEY, Associated Press
Another wave of student walkouts is expected to disrupt classes Friday at hundreds of schools across the U.S. as young activists press for tougher gun laws.
The protests were chosen to line up with the 19th anniversary of the Columbine High School shooting, which left 13 people dead in Littleton, Colorado. At 10 a.m., students plan to gather for moments of silence honoring the victims at Columbine and other shootings.
From there, some students will head to rallies at their statehouses. Others will stay at school to discuss gun violence. Some are holding voting registration drives.
Organizers say there will be walkouts in every state, with more than 2,600 registered on the event's website as of Thursday. Citywide protests are expected to attract thousands in New York City and Austin, Texas. Police in Richmond, Virginia, say they expect at least 10,000 at the state Capitol.
It follows a wave of youth activism that has emerged after the Feb. 14 shooting massacre at Marjory Stoneman Douglas High School in Parkland, Florida.
Tens of thousands of students left class March 14 to protest gun violence in what historians called the largest youth protest movement since at least the Vietnam War. Days later, hundreds of thousands of teens and their backers rallied across the U.S. calling for tougher laws on guns and ammunition.
Plans for Friday's walkout began only hours after the Parkland shooting, when a Connecticut teen started an online petition calling for protests on the anniversary of Columbine. Sophomore Lane Murdock then gathered a few other students at Ridgefield High School to orchestrate the national protest.
They also have received help from Indivisible, a left-leaning nonprofit based in Washington that helps boost grassroots activism. The group says it was formed after the 2016 election to oppose the policies promoted by President Donald Trump.
"We're walking out to remember every single young person who has been killed by American gun violence," Murdock said in a statement Thursday. "We're walking out to talk about the real problems our country is facing, and the solutions that our leaders are too scared to dream up."
Administrators at many schools tacitly allowed the walkouts in March, opting not to punish participants. But some now say the leniency has expired.
At a town hall Monday, the chancellor of New York City's education department urged students not to walk out on Friday.
"You don't need to be out of school all day to make your voices known," Chancellor Richard Carranza told students at Brooklyn Technical High School. "You've already made your voices known. So I'm going to ask you to stay in school."
Even so, students at many New York schools are planning to rally at the city's Washington Square Park.
Some schools in Houston and elsewhere will give students time to share their views but have warned them not to leave campus or return to class late. Some others are holding alternative events after school. Many have simply said students are expected to stay in class throughout the day.
Students in the Washington area are planning to march from the White House to the Capitol building, where they will rally and deliver letters to Congress calling for greater gun control.
In Littleton, some survivors of the Columbine shooting planned to join with Parkland survivors for a vigil and rally Thursday evening. But there will be no walkout at Columbine, which has long canceled classes on the anniversary of the shooting. Instead, students will be called to participate in a day of service.
Principal Scott Christy said in a letter to other schools in his district that April "has long been a time to respectfully remember our loss, and also support efforts to make our communities a better place."