Moral traits and identity were jointly considered toward a developmental understanding of adolescent maturity through volunteerism. In Study 1 (with 1550 urban high school students) moral traits were factor analyzed for developmental and cultural validity. Developmental maturation was implied with the finding that high school seniors scored higher than freshmen on four of five moral trait factors. Factors were regressed on volunteer indices. Adolescents reporting higher levels of moral traits were more involved in volunteer activities. Overall caring-dependable and principled-idealistic moral trait factors were associated with volunteerism. In Study 2 (with 15 exemplar adolescents and 15 matched comparisons) caring-dependable and principled-idealistic moral trait factors were compared with self-understanding narratives in a computational knowledge model. This analysis produced self-understanding schemas by sample group. Exemplar adolescents associated action with personal goals in the self. Findings suggest that traits influence maturing adolescent identity through goal-oriented moral actions which promote purpose and meaning.