Recent theoretical developments in our understanding of developmental trends in adolescent memory, judgment, and decision-making suggest ways in which existing risk reduction programs for adolescents can be improved. Using fuzzy-trace theory, these developments were applied to a validated and evidence-based program, Reducing the Risk (RTR) in a randomized controlled trial. Following a baseline assessment, 734 participants aged 14–19 were randomly assigned to one of three 16 hour interventions—RTR, a modified RTR program (RTR+), or a control condition about improving communication skills. Upon completing the intervention, participants completed a post-survey and were then followed up at three, six, and 12 months later. Primary outcome measures included sexual behavior (initiation, number of partners) and prophylactic behavior (e.g., condom use at last sexual encounter and number of unprotected sexual partners). Discrete time survival analysis revealed that participants assigned to RTR+ were significantly less likely to initiate sexual activity one year after the intervention was administered, and random effects models suggested that RTR+ also decreased the sexual partners across all time points. In addition, RTR+ had significant positive effects on measures of knowledge, intentions, attitudes, perceived norms, self efficacy, perceived behavioral control, as well as on several measures of risk perception suggested by the study’s theoretical framework. Among 23 domains of outcome variables assessed, positive effects of either curriculum were found in 18 domains. Positive effects of RTR+ were found in 16 domains, and positive effects of RTR were found in 12. RTR+ outperformed RTR in 9 of 18 domains (including sexual behavior), and RTR outperformed RTR+ in two domains. The results demonstrate that simple, theory-driven manipulations can be used to improve upon existing evidence-based programs for reducing adolescent sexual risk taking.