4. Identify factors that moderate and/or mediate the effect of the experimental intervention on our outcomes of interest (drug use, engagement in treatment), and estimate their effect sizes. Identifying moderating variables will help us to identify subgroups of optimal responders to the brief intervention. Based on our previous experience, we theorize that girls may respond more strongly to the intervention than boys, and that those who participate in other treatments (outpatient counseling) and/or a laboratory drug testing program will also have greater response.