We invited adolescents to participate in this study through informational and consent letters sent home to parents that were supplemented with follow-up phone calls. Once consent for participation was obtained from parents, we sought and obtained assent individually from adolescents before study enrollment. We conducted individual interviews at study sites, community settings, or participants’ homes shortly after adolescents entered their after-school program (Time 1, baseline), at the end of the program (Time 2, 8 months later), and one year after the initial interview (Time 3, 1 year later). Each interview required about 30–45 minutes to complete for which adolescents received a $40 gift card to a local mall. Attrition rates at Time 2 and Time 3 were 27.6 percent and 38.4 percent, respectively. We found no differences in baseline parental knowledge or adolescent substance use scores between adolescents who completed measures at subsequent time points and those who did not.
