Bilingual education is thought to be one of the principal means of simultaneously revitalizing threatened language and preparing students for success in mainstream society. However, little research has examined, in a comprehensive and longitudinal fashion, bilingual programs in Aboriginal contexts. Hierarchical linear modeling was used to conduct a longitudinal analysis of the language skills of 110 Inuit students participating in an Inuktitut-English/French program in a remote Arctic community. Students' skills in English or French improved from Grades 4-6, after a switch to second language instruction; whereas, their skills in Inuktitut showed no significant improvement across these grades. Baseline heritage language skills in Grade 3 were found to be predictive of later success in both the heritage and mainstream languages, providing evidence for cross-language transfer and pointing to the pivotal importance of heritage language instruction for Aboriginal students. (Contains 3 notes, 5 tables, and 3 figures.)