Academic language skills support mid-adolescents' comprehension of the language of school texts. To date, scarce research has explored associations between dual academic language skills and reading comprehension among mid-adolescent dual language immersion (DLI) students. This study examined individual differences in Spanish and English academic language skills and their contribution to English reading comprehension in a cross-sectional sample of DLI students in Grades 4-6 (N = 101). Taking advantage of a recently proposed construct, the core academic language skills (CALS), and the CALS instruments available in Spanish and English, dual academic language skills were examined as predictors of English reading comprehension. Results revealed that Spanish and English CALS were both significant predictors of English reading comprehension even after accounting for students' sociodemographic background, English proficiency designation, and English word reading fluency. Findings underscore the cross-linguistic contribution of Spanish academic language skills to English reading comprehension and highlight the importance of promoting these skills in both languages to support mid-adolescent DLI students' biliteracy development.