Montreal Longitudinal Study, Canada
The Montreal Longitudinal study was of a school-based parent training that identifies boys with disruptive behaviour in kindergarten but does not work with them until age 7. The 2-year programme then delivered showed positive impact, including lower likelihood of being involved in gangs. Follow-up at age 24 showed that two thirds of the disadvantage of these disruptive kindergarten children had been removed by this 2-year intervention at age 7-9.
"An effective intervention at age 7 was able to remove two thirds of the disadvantage reflected in the behaviour of a group of disruptive kindergarten children."
The objectives of the parenting skills and children's social skills treatment were to employ parent training to reduce disruptive behaviour identified in kindergarten boys of low socio-economic origin, and thereby move them off the trajectory leading from early aggressive, antisocial behaviour to later aggressive, delinquent behaviour. The intervention commenced when the boys were age 7 and lasted 2 years. Follow-up at age 24 showed that two thirds of the disadvantage of these disruptive kindergarten children had been removed by this 2-year intervention at age 7-9.
Summary of findings to age 12
By the end of primary school, the behaviour of the disruptive boys in the untreated group confirmed previous research findings that physical aggressiveness and academic problems, are predictors of delinquency that are identifiable early on in a child's development. The research also confirmed that social intervention can positively affect the social development of disruptive boys.
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), and having friends arrested by the police (no specific statistics provided). Follow-up at age 24 showed lasting effects reflected in significantly higher rates of high school graduation and lower levels of criminality.