Improving the long-term life outcomes of disadvantaged youth remains a top policy priority in the United States, although identifying successful interventions for adolescents--particularly males--has proven challenging. This paper reports results from a large randomized controlled trial of an intervention for disadvantaged male youth grades 7-10 from high-crime Chicago neighborhoods. The intervention was delivered by two local non-profits and included regular interactions with a pro-social adult, after-school programming, and--perhaps the most novel ingredient--in-school programming designed to reduce common judgment and decision-making problems related to automatic behavior and biased beliefs, or what psychologists call cognitive behavioral therapy (CBT). We randomly assigned 2,740 youth to programming or to a control group; about half those offered programming participated, with the average participant attending 13 sessions. Program participation reduced violent-crime arrests during the program year by 8.1 per 100 youth (a 44 percent reduction). It also generated sustained gains in schooling outcomes equal to 0.14 standard deviations during the program year and 0.19 standard deviations during the follow-up year, which we estimate could lead to higher graduation rates of 3-10 percentage points (7-22 percent). Depending on how one monetizes the social costs of crime, the benefit-cost ratio may be as high as 30:1 from reductions in criminal activity alone. [A full list of sponsors of this project can be found on NBER's web site: http://www.nber.org/papers/w19014.ack.]