Students from Marjory Stoneman Douglas High School, where a former student is accused of murdering 17 people on Wednesday, joined others on social media to plan rallies, a Washington march and a national walk-out aimed at getting the attention of an adult population many say has failed to protect them.
"I felt like it was our time to take a stand, because, you know, we're the ones in these schools, we're the ones who are having shooters come into our classrooms and our spaces," said Lane Murdock of Ridgefield High School in Connecticut.
Murdock, a 15-old sophomore who lives 20 miles (32 km) from Sandy Hook Elementary School where 20 children and six adults were shot dead five years ago, drew more than 36,000 signatures on an online petition Sunday morning calling on students to walk out of their high schools on April 20.
Last week's massacre in Florida, which followed several other school shootings this year, inflamed the country's long-simmering debate between advocates for gun control and gun ownership.
Former student Nikolas Cruz, 19, faces multiple murder charges in the deaths of 14 students and three staff members, and the wounding of more than a dozen others, in a rampage that eclipsed Columbine as the country's worst mass shooting at a high school.
The charges can bring the death penalty, but prosecutors have not yet said if they will seek capital punishment.
Cruz was reported to have been investigated by police and state officials as far back as 2016 after slashing his arm in a social media video, and saying he wanted to buy a gun. Authorities, however, determined he was receiving sufficient support, newspapers said on Saturday.
In addition, the Federal Bureau of Investigation admitted on Friday that it failed to investigate a warning that Cruz possessed a gun and the desire to kill.
President Donald Trump lashed out late on Saturday at the FBI for missing signs that could have prevented the shooting, and accused the agency on Twitter of "spending too much time trying to prove Russian collusion with the (2016) Trump campaign."
"You know, we're marching because it's not just schools, it's movie theaters, it's concerts, it's nightclubs," student Alex Wind said on NBC's "Meet the Press." "This kind of stuff can't just happen."
A rally is set for Tallahassee, the state capital, on Wednesday, where a lawmaker is seeking a legislative opening for a ban on the sale of assault weapons, including the AR-15 that Cruz is alleged to have used.
"I think that putting them on record is what needs to be done right now," said Stewart, who said she plans to meet with Douglas High School students in the capital on Tuesday night.