In 2009, researchers in Chicago set out to test a weekly school program for teenage boys called Becoming a Man. They picked 18 schools in some of the city’s most violent neighbourhoods. Some boys were offered a place at random, and the rest weren’t, so the two groups could be compared. By the end of the school year, the boys who took part had been arrested for violent crimes 45 percent less often.

Four years later, they ran the test again with new boys. This time the drop was 50 percent. Both results were published together in the Quarterly Journal of Economics.

So what made the difference? Most people would guess the boys gained self-control or grit, or that having a good mentor helped. The researchers found no sign that any of them explained it. Their best answer is something smaller: the boys learned to stop for a moment before they reacted.

It starts with a ball.

The ball in the fist

Picture a school classroom in Chicago. A group of teenage boys splits into pairs. One boy in each pair gets a ball and closes his fist around it. The other has 30 seconds to get it out.

Almost every boy grabs, pulls and twists. Then the group leader points out the one thing nobody tried. They could have simply asked.

Why not? Most boys say something like “he would have thought I was a punk.” So the leader turns to the boys who held the ball. What would they have done if someone had just asked nicely?

“I would have given it,” they usually say. “It’s just a stupid ball.”

That exercise is part of Becoming a Man, or BAM, run by the Chicago charity Youth Guidance. It borrows from cognitive behavioral therapy, or CBT, which helps people “think about their thinking,” as the paper puts it. Boys met in groups of about eight, for an hour a week, during school. The group leaders were college-educated men, often from neighbourhoods like the boys’ own, who didn’t need training in psychology.

Same result, four years apart

Instead of relying on the boys’ word, the researchers checked police and school records. The first trial included 2,740 boys in grades 7 to 10. The second, from 2013 to 2015, followed 2,064 ninth and tenth graders over two years.

While the program ran, total arrests fell 28 percent in the first trial and 35 percent in the second. Violent-crime arrests fell 45 and 50 percent. The two results were so close the gap could easily be chance. That matters: many youth programs look good once and are never tested again.

Only about half the boys offered a place went to even one session, so these figures are estimates for those who did.

Not grit, and not a mentor

When teenagers go off the rails, people tend to reach for the same few explanations. The researchers checked them, using school surveys about grit, social skills and whether students had an adult at school to talk to. “We find no positive evidence that these effects are due to changes in emotional intelligence or social skills, self-control or ‘grit,’ or a generic mentoring effect,” the authors write.

They admit their “data on mechanisms are not ideal,” with grit measured by just two questions. So grit and mentoring weren’t ruled out. Nothing pointed to them either.

Think back to the ball. Nobody in that room was learning to bottle up his anger or try harder. They were learning to catch themselves acting on instinct.

The moment before a fight

That instinct, the researchers argue, is the key, and it isn’t unique to these boys. All of us often act on autopilot, because thinking every situation through takes effort.

For a boy in a dangerous neighbourhood, one automatic reaction is pushing back hard when challenged. On the street, that can stop him looking like an easy target. The trouble comes when it kicks in somewhere else. Being yelled at by a teacher, the authors write, “may at first glance feel like one’s reputation is being challenged, just as on the street.”

To test the idea, the team played a game with about 490 boys from the second trial. Picture one of them sitting in an empty classroom with a researcher. He is handed an envelope with $10 inside. Somewhere else in the building, he is told, another student is playing too. The two sides will talk over a walkie-talkie.

The walkie-talkie crackles. His partner, the voice says, has decided to take $6 of his money. Then it is his turn. The partner now has $10 of his own. How much of it does the boy want to take?

In reality, there was no other student. The voice was a researcher reading from a script.

Boys who hadn’t been through BAM made up their minds in about 1.1 seconds. Boys who had took about 80 percent longer. But they didn’t take much less money. The program hadn’t made them nicer. It had made them stop before they answered. It’s one experiment, and the authors call it “suggestive support,” not proof.

Gains that faded

The drop in arrests was measured while the program was running. Only the first trial kept tracking the boys afterwards, and the paper says plainly that the effect on arrests “did not persist beyond the program period.” What did last was school: boys who took part were 6 to 9 percentage points more likely to graduate.

The University of Chicago Crime Lab, which ran the research, tested BAM twice more between 2013 and 2015. Those trials didn’t go as well. In a technical appendix to their working paper, the team describes one as “more mixed” and the other as showing “signs of null-to-adverse effects.” The one thing that lined up with the weaker results was how many young people were in BAM across Chicago that year.

Youth Guidance says BAM now runs in eight cities. In late 2025, the mayor’s draft budget cut its Chicago funding, until city council members put back $3.5 million.

Ten years later, in Liberia

A study from West Africa adds a twist. In Liberia’s capital, Monrovia, researchers found 999 men involved in crime and violence. Some got eight weeks of CBT-style therapy. Some got a $200 grant, about three months’ wages. Some got both, and some got nothing.

At first, therapy on its own cut crime and violence, then faded, much as in Chicago. Ten years later, though, men who had had the therapy, with or without cash, were about half as likely as the others to rob, sell drugs or get into street fights. Most experts asked beforehand had expected the effects to disappear or shrink a lot.

Why did it last there but not in Chicago? Nobody knows. These were grown men in a different program, and the results come from their own survey answers, not arrest records.

But the two studies share an idea, and it isn’t toughness or a mentor. It’s about learning to pause, just for a moment, before you react. As the Crime Lab puts it, “Most homicides in the United States start with words.” A pause at the right moment might be enough to stop them going any further.