This study investigated code-mixing practices, specifically the use of L2 (English) in an L1 (Chinese) class in a U.S. bilingual program. Our findings indicate that the code-mixing practices made and prompted by the teacher served five pedagogical functions: (a) to enhance students' bilingualism and bilingual learning, (b) to review and consolidate content taught in the ESL and all-English classes, (c) to facilitate cross-linguistic transfer, (d) to increase understanding of home and U.S. cultures, and (e) to foster an understanding of cross-cultural differences. In particular, these functions encompass lexical, cross-cultural, and cross-linguistic dimensions. Findings suggest that strategic use of code-mixing of bilinguals' L1 and L2 in instruction may enhance students' bilingual development and maximize their learning efficacy.