Developing spelling skills in English is a particularly demanding task for Chinese speakers because, unlike many other bilinguals learning English as a second language, they must learn two languages with different orthography as well as phonology. To disentangle socioeconomic and pedagogical factors from the underlying cognitive-linguistic processes that predict the development of spelling, we used a 6-month longitudinal design and compared children with English as their first language (English-L1; n = 50) and children with Mandarin as their first language (Mandarin-L1; n = 50) from the same kindergarten. Both groups were tested on parallel versions of English and Mandarin tasks as predictors at Time 1, and their spelling sophistication scores were then computed from a 52-item experimental task administered at Time 2. After we controlled for nonverbal IQ, age, vocabulary, and spelling achievement on Wide Range Achievement Test 4 at Time 1, regression analyses showed that phoneme awareness was the strongest predictor of spelling sophistication for English-L1 children, but syllable awareness and letter-sound knowledge were also important for Mandarin-L1 children. The implications of these differences in the cognitive-linguistic processing of bilingual children learning two dissimilar languages are briefly discussed. (Contains 5 tables.)