Hope is a motivational factor that helps initiate and sustain action toward long-term goals, including flexible management of obstacles that get in the way of goal attainment. Despite an abundance of research on the benefits of hope, little attention has been given to this aspect of youth development via longitudinal studies. In this study, we collected ratings of hope and positive and negative affect from 975 adolescents over a six-year assessment period (Grades 7–12). Using cross-lagged structural equation modeling, we found that hope led to greater positive affect, with little evidence for the reverse direction. In contrast, hope and negative affective states were reciprocally related. Hope predicted future well-being particularly well in years when the young people where in transition (e.g. starting high school and transitioning to senior high school). Our data support the position that hope is a malleable attribute that fosters positive youth development.