Tremblay – Montreal longitudinal experimental study

The Montreal longitudinal experimental study is a study of boys who were in kindergarten in low socio-economic areas of Montreal in the early 1980s. These boys are now 26 years old and we have assessed them almost yearly since they were in kindergarten. It’s a sample of approximately 1000 boys. The aim of the study was to understand the development of children who are at risk of having serious problems during adolescence. That’s why we chose boys and that’s why we chose them in a large city and from low socio-economic areas. The study has focused on a large range of topics, but one of the main focus was how can we prevent children who are at risk when they enter kindergarten from having serious problems in elementary school and then through the adolescent years.  

We have shown with this study that probably children are at their worst in terms of aggression, hyperactivity. If we start in kindergarten, they are at their worst in kindergarten and most children as they grow older tend to reduce the frequency of their problem behaviors. But if they don’t substantially reduce that level of problem behavior then they get into more problems in terms of the reactions to their behavior because they’re growing taller and stronger and people will not put up with an aggressive, physically aggressive 12-year old as they will put up with a five or six-year old aggressive child.  

We did a prevention experiment with that study, so we gave parent training and social skills training to the at-risk children and the at-risk were of course those who showed most problems in kindergarten. And we’ve shown that an intervention, an intensive two-year intervention, with these highly disruptive boys in kindergarten, could reduce their level of problems later on. Those who received the intervention were more successful in school, they had friends who were more positive, less of them abandoned school before the end of high school and less of them had serious delinquency problems.