The “treatment theory” underlying MST draws upon social-ecological models of behaviour and causal modelling studies of serious antisocial behaviour in youth.

The social-ecological model depicts the process of human development as a reciprocal interchange between the individual and "nested concentric structures" that mutually influence one another. Extrafamilial systems, such as school, work, peers, and even community and cultural institutions are seen as interconnected with the youth and his or her family.

Importantly, this ecological view that behaviour is multi-determined is strongly supported by causal modelling studies of youth antisocial behaviour that have been conducted over the past 20 years. These studies indicate that a combination of individual, family, peer, school, and neighbourhood factors are linked with serious antisocial behaviour in adolescents.

Problem behaviour may be a function of difficulty within any of these systems and/or difficulties that characterize the interfaces between these systems (e.g., lack of family-school relations, conflictual family-neighbourhood relations). Thus, consistent with both the empirically established determinants of serious antisocial behaviour and with social-ecological theory, the scope of MST interventions target problems within multiple systems, as well as the linkages between these systems.