Final answer:
The counselor assessing Brian should first consider his familial relationships and social milieu, as these factors are vital in understanding and addressing his chemical dependency and associated behaviors.
Step-by-step explanation:
In assessing Brian, a 15-year old boy admitted to a program for chemical dependency with a history of running away from home, erratic school performance, and arrests for petty theft, the counselor should first consider Brian's familial relationships and social milieu. Understanding his home environment and social context is crucial because family dynamics and peer influence are often key factors in adolescent behaviors and can significantly impact treatment outcomes. As shown by the research in the Journal of Psychoactive Drugs, family factors are closely related to substance use changes in adolescents. Additionally, assessments of social resources and goals are important, but they are generally considered after establishing the context in which the problematic behaviors are occurring.