This study examined whether age differences in risky decision making are dependent on known probability and value of outcomes (i.e., the expected value [EV]), the valence of anticipated outcomes (gains or losses), and individual differences in working memory and impulsivity. We used a task that varied risk independently from EV so that taking risks could be advantageous or disadvantageous. Results indicated differential developmental courses for the sensitivity to EV and outcome valence from early to late adolescence. An increase in risk-advantageous but a decrease in risk-disadvantageous behavior was obtained between early-to-mid and late adolescence. All adolescents showed higher risky behavior when losses rather than gains were expected. Age differences in the sensitivity to EV were fully mediated by individual differences in working memory but not by self-reported impulsivity, suggesting that decision making under known risk is strongly limited by the maturation of cognitive control processes.