This research investigated the potential contributions of natural mentoring relationships and ethnic identity to the academic attitudes and performance of Latinx high school students. In a sample of 347 urban Latinx students in grades 9 and 10, analyses examined the presence and quality of mentoring relationships as well as ethnic identity exploration and affirmation as predictors of changes in grade point average and the perceived economic value of education. Analyses included tests for a hypothesized role of ethnic identity in mediating associations of mentoring measures with the academic outcomes. The presence of a mentoring relationship was not significantly related to ethnic identity or change in academic outcomes over time. However, mentoring relationship quality was associated with a more positive ethnic identity, and support was found for the hypothesis that ethnic identity mediates the association between the quality of mentoring relationships and change over time in the economic values toward education among Latinx adolescents. Study findings suggest the importance of supportive adults in the ethnic identity and academic outcomes of Latinx adolescents.