This study explored effects of Spanish oral language skills (vocabulary and syntax) on the development of English oral language skills (vocabulary, morphology, semantics, syntax) and reading comprehension among 156 bilingual Latino children in second through fifth grade whose first language was Spanish and whose second language was English. Using a cohort-sequential design (Cohort 1: second-third grade; Cohort 2: third-fourth grade; Cohort 3: fourth-fifth grade), we estimated Grade 2-5 trajectories of English oral language skills and reading comprehension. We assessed whether early levels of Spanish vocabulary and syntax predicted: (a) students' fifth-grade English oral language skills and reading comprehension; and (b) students' Grade 2-5 growth in these skills. Results showed that Spanish syntax predicted all Grade 5 English oral language skills and reading comprehension. Spanish syntax was also positively related to growth in English semantic knowledge. Spanish vocabulary was not associated with any English oral language skills or reading outcomes. Theoretically, results suggest that explorations of "transfer" from Spanish to English are likely moderated by the constructs under study and the means by which they are operationalized. Instructionally, working with bilingual learners around issues related to Spanish and English syntax has implications for bilingually and metalinguistically oriented teaching approaches that may build linguistic knowledge and promote reading comprehension.