This article examines the reported language ideologies and family language policies of the parents of Cantonese-English bilinguals in the U.S. in relation to their children's achievement scores in Cantonese and English. We explore the relationships first by language of instruction. Results show children in bilingual classrooms scored higher than those in mainstream (English-only) classrooms on the Cantonese tasks, but significantly more children in bilingual programs had Cantonese as a home language than children in mainstream classrooms. Parents from mainstream classrooms were significantly more satisfied with their children's English-language attainment than parents from bilingual classrooms. Using cluster analysis, we then identify four new groups of children based on their language proficiency: (a) English-dominant, (b) Cantonese-dominant, (c) "balanced bilingual," and (d) "ideal bilingual." Results show all children scored at or above the monolingual English mean on English decoding, but the ideal bilingual cluster had the largest Cantonese vocabulary. The English-dominant group heard significantly less Cantonese in the home, while all children in the ideal bilingual and Cantonese-dominant clusters heard only Cantonese. Findings point to the integral component of the family unit in children's bilingual development and bring up timely issues relating to family language planning and policy. (Contains 4 tables, 1 figure and 4 footnotes.)