Conducted a longitudinal-experimental study to describe the Cossack interactions of disruptive boys during the primary school years, and also verify the effects of both parent training and children's social skills training for the prevention of delinquency behavior; the study's population consisted of kindergarten boys from low socio-economic areas of Montreal; 1,034 subjects were retained for the longitudinal study; this total sample has been followed early from age 10 onward.