The Preventive Treatment Program (also known as the Montreal Longitudinal Study and the Montreal Prevention Experiment) was aimed at disruptive kindergarten boys and their parents, with the goal of reducing short- and long-term antisocial behavior. This program targeted white, Canadian-born males ages 7 to 9, from low socioeconomic families, who were assessed as having high levels of disruptive behavior in kindergarten. The program provided training for both parents and boys with the long-term goal of decreasing delinquency, substance use, and gang involvement. The program was administered to the treatment boys and their parents when the boys were 7 years old and lasted until they were 9.

The goal of this program is to reduce short- and long-term antisocial behavior.

Evaluations have demonstrated both short- and long-term gains for youths receiving the intervention.

At age 12, 3 years after the intervention,
- Treated boys were less likely to report the following offenses: trespassing, taking objects worth less than $10, taking objects worth more than $10, and stealing bicycles.
- Treated boys were rated by teachers as fighting less often than untreated boys.
- 29 percent of the treated boys were rated as well-adjusted in school, compared with 19 percent of the untreated boys.
- 22 percent of the treated boys, compared with 44 percent of the untreated boys, displayed less serious difficulties in school.
- 23 percent of the treated boys, compared with 43 percent of the untreated boys, were held back in school or placed in special education classes.

At age 15, those receiving the intervention were less likely than untreated boys to report
- Gang involvement
- Having been drunk or taken drugs in the past 12 months
- Having committed delinquent acts (stealing, vandalism, drug use)
- Having friends arrested by the police