This study adds to the limited research on the potential importance of the quality of the relationship between adult prevention service providers and youth participants in enhancing social skills and strengthening prevention outcomes. Study subjects were drawn from seven prevention programs funded under a Youth Mentoring Initiative by the Center for Substance Abuse Prevention in the Substance Abuse and Mental Health Services Administration. These programs maintain a relationship-based service focus but use a variety of one-on-one, group, volunteer, and paid staff service formats. Study results showed that youth who perceived a higher level of trust, mutuality and empathy in their relationship with providers experienced significantly greater improvements in social skills (i.e., cooperation, self-control, assertiveness, and empathy) than program participants who perceived a lower quality relationship with adult providers. These findings underscore the importance of recruitment, training and supervisory practices that promote staff and volunteer skills in achieving high quality relationships with youth participants regardless of the specific intervention strategy. Editors' Strategic Implications: Practitioners and policymakers should review the authors' findings about the importance of individual adult skills in building protective mentoring relationships. The impact of relationship quality, rather than setting, suggests that the scope of effective prevention practice can be broadened beyond the confines of formal prevention programming to any place in which caring and skilled adults interact with youth.