This preregistered, longitudinal study examined how much adolescents value and integrate their parents' and peers' attitudes into their own attitudes from early to middle adolescence. Across three waves, participants (N = 172, 91 female, 11-16 years across three waves; 439 data points) decided whether to pay money to learn their parents' or peers' attitudes about externalizing behaviors. Multivariate growth models revealed that adolescents were consistently willing to pay money over time to learn their parents' and peers' attitudes. The value of learning peers'--but not parents'--attitudes predicted changes in personal attitudes during adolescence, and this did not change across age. Moreover, the effect of others' attitude value on social influence weakened from early to middle adolescence, such that early adolescents who highly valued learning the attitudes of others (i.e., paid more) tended to shift their own attitudes more toward those endorsing positive influence, regardless of the source. In contrast, early adolescents who valued learning others' attitudes less were less susceptible to positive social influence. Importantly, this effect went away in middle adolescence. Although adolescents are highly motivated to learn their parents' and peers' attitudes about externalizing behaviors, how much those attitudes inform their personal attitudes depends on the source of input and the age of adolescents.