The present study examined consistency and inconsistency in adolescents' ethnic identification (i.e., self-reported ethnicity) across the 6 middle-school semesters. The sample (N = 1,589, of whom 46% were boys and 54% were girls) included African American, Asian/Pacific Islander, Caucasian/White, Latino/Latina, Mexican/Mexican American, and multiethnic students. Latent class analyses yielded 3 key patterns in ethnic identification across the middle-school years: consistent, late consistent, and inconsistent. Ethnic identification remained consistent across fall and spring of 6th, 7th, and 8th grades for only about 60% of the students. Asian/Pacific Islander students were more consistent, and multiethnic students were less consistent than students from other ethnic groups. School ethnic composition was associated with systematic shifts in ethnic identification from the beginning to the end of middle school for those students who initially identified as Latino/Latina, African American, or multiethnic but not for Mexican-origin students. In combination, the results provide insight into the consistency of ethnic identification, the role of context in adolescents' self-representation, and considerations for longitudinal studies that examine ethnic differences. (Contains 3 tables and 2 figures.)