Proficient writing performance in English requires multiple cognitive skills, which can be particularly challenging for English Learners (ELs). However, compared with reading and mathematics, there have been fewer scientific inquiries that explore the relationship between cognitive components and writing. The purpose of this study was to examine the role of three cognitive components (phonological awareness [PA], oral language development [OLD], and working memory [WM]), on writing development in Spanish-speaking EL children. To achieve this goal, 374 children in Grades 3 to 5 were administered a battery of cognitive measures in both Spanish as well as English, and a narrative writing task in English. Using structural equation modeling, three important findings emerged. First, the results showed that PA in both Spanish and English positively predicted English writing performance. Second, English OLD had a positive effect on writing, but Spanish OLD was a negative predictor of writing. Third, WM in both languages had large positive effects on writing in English. Taken together, the findings from this study highlight the important roles first- and second-language PA, OLD, and WM play in upper elementary ELs' English writing.