Three weeks after a former student had shot seventeen pupils and staff at Marjory Stoneman Douglas High School, and three days after classes had resumed, the campus was settling into a routine again. A few patrol cars and a small squadron of sheriffs on motorcycles were all that remained of the police presence. The sign-waving supporters outside were gone, and the farm animals trained in emotional support had returned to their paddocks. By the time the school bell rang on Friday, at 7:40 A.M., the one television crew on site was breaking down its tripod. Outside the school fences were piles of rotting flowers, Teddy bears, deflated Mylar balloons, and pinwheels spinning in the sun. What had begun as an emergency was settling into finality.

In the days leading up to the Stoneman Douglas students’ return to school, the movement for gun control they had started had grown far beyond the city, out in the world. The teen-age activists had tolerated expressions of empathy from daytime talk-show hosts (Dr. Phil and Ellen DeGeneres) and lame jokes from the nighttime ones (Jordan Klepper and Bill Maher). John Legend and Chrissy Teigen, George and Amal Clooney, Oprah Winfrey, and other celebrities had made large donations for the upcoming march on Washington. As bereaved parents gave furious speeches at the Florida statehouse, where the legislature was considering a school-safety bill, a delegation of Stoneman Douglas students travelled to Washington, D.C. They met with the Speaker of the House, the House Minority Leader, and the Florida congressional delegation, all of whom afterward posted photos on social media of themselves engaged in thoughtful conversation at conference tables. The students posted photos of themselves with Congressman John Lewis, of Georgia, the civil-rights leader, and with the Vermont senator Bernie Sanders.

Emma González, one of the student leaders, hadn’t joined the delegation to Washington, but had stayed at home to work on recruitment for the March for Our Lives, to be held on March 24th, in Washington. The afternoon of her third day back at school found her in the gymnasium of the recreation center at Pine Trails Park, preparing for an information session. Since her return to school, González had dedicated herself to selling the march to her fellow-students. This meant sharing Never Again’s platform about gun control, while also being sensitive to a wide range of political viewpoints. At a meeting the previous day, some students expressed worry that the march’s message was too partisan.

“These are my opinions,” González said to Jeffrey Foster, her A.P. Government teacher, who was there to answer questions from parents. “I’m, like, you can say whatever you want about whatever topic, I’m not telling you what to say there, but make sure the message is cohesive. Here’s how I feel, and here is what goes through my head. You don’t have to listen to me on this, but if you want to help this is a really important way to help.”

The gym had been stocked with pizzas, boxes of tissues, and coolers of drinks. Students arrived, many of them accompanied by their parents, and took their seats. González checked to make sure that bottles of water and paper plates had been put out. She wore a maroon sundress and pink sneakers. Less than two weeks before, I had watched as she sat at a picnic table and chose a Twitter handle. Now she had more than a million followers on Twitter—more, as many pointed out, than the N.R.A. But all of this had happened outside of school. I asked how it was to be back.

“It’s pretty good,” she said. “And if news developments happen in the day—like today, when we found out about the shooting, my friend got upset, and I was immediately able to talk to her. I didn’t have to drive over to her house or run over there, like, she walked down the hallway and we were able to talk to each other. That’s nice. And the support dogs—have you heard about the support dogs?”

The shooting that day had happened at Central Michigan University, where a nineteen-year-old named James Eric Davis, Jr., had killed his parents, who had arrived to pick him up for spring break. For González and the other students, the news of yet another act of gun violence on a campus had renewed their sense of purpose but also their feeling of powerlessness.

“It feels like we’re not getting anything done,” González said. “The wheels of bureaucracy turn so slowly that, no matter what we say and how many people we get to sign petitions, we can’t vote anybody out until midterm elections, which are so far away.” As February gave way to March, two points were proved about the gun-control debate: first, that cynicism about it was not unfounded; second, that, even as the students advocated, the violence would not stop.

To insure that students would be comfortable asking questions, the media were not allowed to remain in the gym for the lecture, so, as González dimmed the lights and began her presentation, I stepped outside. Near the entrance of the rec center, Ryan Deitsch and Delaney Tarr, who had been among the students who went to Washington, D.C., earlier in the week, sat at a table. Never Again had developed a platform, the main tenets of which Tarr read out to me from a yellow notebook with the words “Anything Is Possible!” embossed on the cover in gold.

“Of course, the assault-weapons ban is the most difficult, and that’s the longest-term thing,” she said, flipping pages until she found her list. “But now what we’re really getting into is universal background checks. That would also entail closing the gun-show loopholes, closing straw purchases, and instilling the red-flag system. We also want to get rid of high-capacity magazines, and we want to raise the age from eighteen to twenty-one.” In Washington, particularly when talking to pro-gun politicians, the students focussed their arguments on narrower problems: the law that forbids the Bureau of Alcohol, Tobacco, Firearms, and Explosives from creating a searchable database; the Dickey Amendment, which prevents research that advocates or promotes gun control; bump stocks, which allow a semiautomatic weapon to fire at a rapid clip. The students became increasingly adept at identifying political obfuscation: the congressman who might discuss “extensive background checks” rather than universal ones; the congresswoman who brings up mental illness to change the subject from gun control. With Senator Charles Schumer, of New York, they discussed the flaws of the background-check system, and how to improve the original assault-weapons ban, from 1994, which Schumer co-authored, and which the students think could be more effective with the addition of a gun-buy-back program.

I asked what it was like to go back to school. “Boring,” Deitsch said. “It’s been coloring and Play-Doh.” Classrooms had been supplied with games and something called “kinetic sand” to ease the students’ reëntry. “When you sit down with the Speaker of the House and then you’re told to just play with a lump of clay, it’s not really stimulating.”

The Speaker of the House, it turned out, had given the students some pushback on their critique of the Dickey Amendment, and a hallway encounter with Congressman Darrell Issa, of California, had turned downright contentious. The Democrats had been more amenable, but, after speaking to them, the movement added another message. “We also wanted to tell them, ‘Listen, we’re so grateful for the help and everything, but we’re not your pawns,’ ” Chris Grady, a Stoneman Douglas senior who went on the trip, said later, after the meeting in the gymnasium. “Make no mistake about it: we’re our own movement.”

The following evening, the second annual Obama Roosevelt Legacy Dinner, advertised as one of the “premier events for the Broward County Democratic Party,” was held at the Pier Sixty-Six Hotel, in Fort Lauderdale. Valets waved attendees into parking lots that overlooked a marina filled with gleaming white yachts. The dinner, tickets to which cost a hundred and seventy-five dollars or more, had been planned long in advance of the shooting, but the agenda had shifted. Bowls of ribbons in Stoneman Douglas colors were available for guests to pin to suit lapels and sequinned cardigans. The crowd was friendly, mostly over the age of forty, and clad in sensible shoes. The yachts outside likely belonged to other people; Mar-a-Lago was a county away. Several Stoneman Douglas students had come to the fund-raiser, too, although not, they emphasized, to endorse a particular candidate. If anything, it was the politicians who wanted their photos taken with the students. In their cocktail-hour soapbox speeches, the Democratic candidates for Florida’s 2018 gubernatorial race emphasized their records and sentiments on gun control. Afterward, a host encouraged guests to proceed to dinner in a “blue wave.”