When people reflect on their important values, they may become more attuned to the needs of others. Two longitudinal field experiments examined whether a subtle value-affirmation manipulation can initiate relatively enduring increases in young adolescents' prosocial feelings (Study 1; M [subscript age] = 12.9) and prosocial behaviors (Study 2; M [subscript age] = 12.9). Participants completed a brief writing exercise that affirmed the values they deemed either most important (value-affirmation group) or unimportant (control group). As predicted, the value affirmation, coupled with a booster affirmation 6 weeks later, caused increases in prosocial feelings and behaviors over the 3-month study period. Antisocial students who were value-affirmed showed especially strong increases in prosocial behavior. These results suggest that "gentle passions" can be aroused in youth by cost- and time-efficient means. The practical utility of value affirmations will need to be evaluated in future work. (Contains 1 table, 1 figure and 1 footnote.)