While the study involved only boys in Montreal, the researchers note that the juvenile justice system in the province of Quebec has a reputation of being among the best.
“The more intense the help given by the juvenile justice system, the greater was its negative impact,” Tremblay said. “Most countries spend considerable financial resources to fund programs and institutions that group deviant youths together in order to help them. The problem is that delinquent behavior is contagious, especially among adolescents. Putting deviant adolescents together creates a culture of deviance, which increases the likelihood of continued criminal behavior.”
Tremblay and colleagues analyzed data on 779 boys from 53 schools in poor neighborhoods. The boys were interviewed every year from age 10 to 17.
By their mid-20s, some 17.6 percent of participants ended up with adult criminal records including homicide (17.9 percent); arson (31.2 percent); prostitution (25.5 percent); drug possession (16.4 percent) and impaired driving (8.8 percent).

See the full article from “U.S. News & World Report”