Knowledge of the factors that influence youths' choice of racial or ethnic labels will help us understand intragroup diversity, suggest ways in which school social workers can support youth's ethnic identity development, and learn if youth who choose different combinations of labels may be grouped together for research purposes. This study of 2,857 Mexican-origin youth in the U.S. Southwest found that linguistic acculturation, socioeconomic status, and educational aspirations are related to choice of ethnic labels. Implications for social work interventions in schools and for future research are offered.