Once a week, J.B. goes to a group-therapy session tailored for teenagers who have been traumatized so often that trauma is taken for granted. “It becomes so normal for a peer to die,” said Amanda Whitlock, the vice president of behavioral health services at Children’s Home and Aid, one of the largest social service providers in Illinois, which operates the therapy program. “The kids say, ‘I know X amount of people who have been shot.’” Someone dies, she said, the kids pull out their phones, get a shirt made for the funeral, tie balloons around the block and move on.

“My boys say they will be dead by 21,” said Mashaun Alston, who leads one of the groups. As Ms. Whitlock put it, “Why would I not do what I want to do if I’m not going to be alive by 21?”

The therapy sessions challenge this fatalism by showing these adolescents how their traumatic experiences are running their lives — how “emotional leftovers” can lead them to automatic behavior that makes things worse. The sessions give them tools they can use to slow down and think through their options in times of stress.

Does it work? The Crime Lab at the University of Chicago is conducting a random-control trial to evaluate this strategy. The lab, as its director, Jens Ludwig, explained, has a decade-long track record of “doing good science that is focused on solving the city’s problems, like reducing gun violence and reducing dropouts, rather than just publishing in journals, the usual orientation of academics.”