This study examined the performance of Mandarin-speaking students in a K-Grade 4 50/50 Chinese/English bilingual program. The program was intended to facilitate students' learning of English and their adjustment to English-medium instruction within the school context. The bilingual-program students were compared to students from Mandarin-speaking backgrounds whose school instruction was conducted totally in English but who attended a weekly 2.5-hour Chinese language class conducted outside of the regular school day through the International Languages Program funded by the Ontario government. Students' abilities in phonological awareness, vocabulary knowledge, morphological awareness, and word reading were measured. Results showed that students in the bilingual program who received less English instruction overall performed comparably in all English measures to their peers in the English-only programs. Some differences in favour of the bilingual-program students were observed in Chinese language and literacy measures, specifically in character recognition. Students in the bilingual program performed above grade norms on standardized measures of English literacy skills and in the Grade 3 provincial standardized testing of English reading and writing abilities.