This dynamic can be demoralizing for the people working without recognition. Bria Smith, 17, from Milwaukee, said she had spent a year working with local nonprofits and Black Lives Matter, but felt no one was listening. “Why would I do so much work and give so much energy of myself to a city that doesn’t care if I’m doing it in the first place?” she asked.

Then she spoke at the March for Our Lives rally in Milwaukee, which led to a seat on a panel when the bus tour went there. Afterward, she recalled, an organizer asked if she wanted to join for more stops. (Her reply: “Give me a second. I have to call my mom and ask her first.”)

Ms. Smith used to see Milwaukee as a prison to escape. But now, “I’ve met so many different youth who had wanted to make a difference in their communities, but never knew how to use their voice and their platform to do that,” she said. “So after Road to Change, I’m going to come back, and I’m going to go to Milwaukee, and I’m going to be that voice for all the people who felt hopeless.”

This is the biggest change of all. The students defined the problem itself differently, as gun violence writ large: not just mass shootings but gang killings, police brutality, domestic abuse, suicide. They talked about sharing their platform and using it to “raise the voices” of the activists who have been organizing in obscurity — several of whom, like Ms. Smith and Mr. Contreras, joined the tour. They tried to build infrastructure everywhere they went, coordinating with local people who would continue the work when the bus was gone.