The effectiveness of various strategies for educating the growing U.S. population of English language learners (ELLs) has attracted a great deal of controversy. Bilingual education theory posits that retention and continued development of native language (L1) skills facilitate academic achievement through two mediating mechanisms. First, L1 proficiency promotes second language (L2) acquisition, which is required to succeed academically. Second, competence in the heritage language positively influences academic achievement by maintaining self-esteem. Both of these meditational chains were tested in a multivariate latent growth model of longitudinal data from the National Education Longitudinal Study (NELS:88/2000). L1 proficiency was specified to predict distal math and science outcomes through its association with both L2 literacy and self-esteem. In turn, academic self-concept was hypothesized to mediate the self-esteem-academic achievement relation. Home and school characteristics were included as covariates. The full model exhibited excellent fit only in the Hispanic portion of the ELL sample. Consistent with the broader literature, ethnicity appears to serve as an important moderator of the way native language proficiency relates to self-perception, L2 acquisition, and math and science achievement. (Contains 5 tables, 3 figures and 1 footnote.)