Invited and sometimes self-invited, teens from across the country hopped on a bus carrying students from Marjory Stoneman Douglas High in Parkland FL, on a 59-day tour of some 80 cities and towns in two dozen states that ended Sunday.

I followed the group on the last three days of the campaign. Here are portraits of four of the students.

Jaclyn Corin, Parkland, FL

Today, Stoneman Douglas students returned to class in Parkland, FL. Jaclyn Corin is senior class president, and last year was junior class president, too. When the Valentine's Day shooting happened, she had been delivering carnations sold to fund the junior prom. Now, she naturally assumed the leadership of the Parkland anti-gun violence movement.

On Sunday in Newtown, CT, where the bus tour ended, Corin sounded hopeful about the November elections but knowing about the difficulty of changing U.S. gun laws significantly. "It's going to take a cultural shift," she said. "And a cultural shift always takes a generation or two. I hope my kids know we don't need weapons of war on the street."

We spoke by phone late this morning. Corin was in the cafeteria for lunch, surrounded by friends. It's hard to escape the memory of what happened given the swarm of reporters on the street, that Building 1200 — where 17 of their classmates and teachers were murdered — is within eyesight, though closed — and that teachers, too, are dwelling on the shooting.

• "Unfortunately teachers are immediately saying where you can hide, and how the alarm system is going to work this year," she said. "I just got out of Holocaust History. And the teacher — four kids died in her class, and she identified herself as just that and how she risked her life to save others. She talked about whether the windows were bulletproof."

Bria Smith, Milwaukee, WI

Bria Smith is 17 and says she grew up with gunshots outside her window as "conditioned reality" in Harambee, on Milwaukee's north side. "But it shouldn't be," she told me Friday in New York.

What happened: Smith got on the bus, invited by Corin, when it passed through Milwaukee. A powerful orator, speaking in bursts, she calls herself an "advocate," among other things serving on the city Youth Council in order to help .

• But until now, she was "really upset that no one would listen."

Smith feels lucky — through a state integration program, she has spent her entire education in well-resourced, mostly white schools in the suburbs, giving her "the biggest impact of my life."

• But she was ready to return home "to help black and brown youth." "I'm only 17," she said on the stage in Manhattan. "None of us should even be up here."

Alex King, Chicago

"This is the generation that says 'enough is enough,'" says Alex King, of Chicago's North Lawndale neighborhood, on the west side. "When we saw something was wrong, we said, 'This is wrong.'"

King was bullied in school and has seen much death around him, most recently that of his 16-year-old nephew, who was killed a year ago. But he has joined the Peace Warriors, a group that tries to reduce violence by championing the teachings of Martin Luther King.

• At 18, King was one of the oldest youth on the tour. In high school, he long had ambitions in drama, but his high school — North Lawndale College Prep — had no money to put on any plays. "There were talent shows and I was always picked as the emcee because I always had a thing for talking in front of large groups of people," King told me.
• This fall, he will be a theater arts major at Grand Valley State University, a 20-minute drive west of Grand Rapids. Is he angry with generations before his own? "The world we are living in shouldn't have to be the world like this," he said.

Ramon Contreras, Harlem

In Harlem, where he moved as a boy, Ramon Contreras runs a group called Youth Over Guns. In March, he helped to organize a walkout along with students across the country, organized by the Parkland group, but decided that media attention was going heavily to white students.

• So on June 2, he helped lead a protest in which thousands of people marched across the Brooklyn Bridge in support of gun control. The Parkland group noticed and tweeted at him. He ended up getting on the bus in Chicago at the very start of the tour on June 15.
• "We want to be the generation to end gun violence," he told me. Did he think they would succeed? "You have to be optimistic that you can. But if we don't succeed, it will go to the next generation. We will pass the baton."

Go deeper: There is already a "Parkland effect"