This article presents a mixed-methods case study of Diego, a bilingual teen who completed public school in Florida. During adolescence, Diego negotiated multiple identities: successful student, Mexican American, bilingual, and typical U.S. teenager. Diego provided interviews and bilingual (English/Spanish) writing (narrative/expository) in 2008 (at age 12, Grade 6) and in 2012 (at age 16, Grade 10). A qualitative analysis of his interviews and a quantitative linguistic analysis of his writing reveal central elements of Diego's language development as related to academic English and identity. Educational implications for working with bilingual adolescents are discussed.