In the area of special needs, children with externalizing behaviour problems face challenges in relationships and social interactions that put them at risk for problems throughout their lives. This study observed the interactions of 6 non-parental adults with 15 children with externalizing behaviour problems and looked at which of the components of the interactions were most related to adults successfully reducing problem behaviours. The research took place at a children's mental health centre and for 8 weeks, and observed weekly group therapy sessions at the agency. There were three groups observed. The specific focus of this study was on examining how the responsiveness of the adults was related to decreases in problem behaviours of the children. The adults who were observed to be most successful were adults who were high and consistent responders to child initiations and high on positive adult initiations. These adults were also high and consistent on responsiveness to problem behaviours. Other results relating to adults' responsiveness and group dynamics are discussed in detail. The findings indicate that is not enough for adults to simply reinforce or punish undesirable behaviours in children, but the best results in both problem behaviours and reciprocal social skills are achieved when adults and children form a positive relationship with each other.