PROJECT SUMMARY The goal of this cross-sectional project with a pre- and post-test design is to determine the contributions of children’s knowledge of Spanish and English languages to English reading achievement in dual language learners (DLL), who constitute 20% of the school-aged population in the United States. Reading difficulties have been linked to detrimental education and life outcomes. Despite the growing demographic and the known challenges associated with reading, little research has been devoted to systematically investigate the predictors of DLLs’ second language reading (in this case, English) development. Language skills are critical to reading success, and our research also demonstrates that language contribute more to reading for DLLs than for monolingual children in upper elementary grades. However, it remains unknown how the various components in DLLs’ two languages contribute to their English reading development, whether the language-reading relationship differs for DLLs of varying degrees of oral language proficiency, and whether the language-reading dynamics change over time for DLLs in different stages of reading development. The current study aims to address these gaps by utilizing multiple measures of language and reading and a cross-sectional design with pre- and post-test data following DLLs over a period of 4-6 months. The study will include 300 Spanish-English DLLs of varying degrees of English language proficiency. All DLLs will be from Spanish-speaking households who learn English as a second language. There will be a total of four cohorts. Cohort One and Two will be in 1st and 3rd grade, respectively, at Time One of the study, and will be followed over a period of 4-6 months in Year One to determine the developmental trajectories of their language and reading and the contributions of language to reading over time. Cohort Three and Four will also be in 1st and 3rd grade in the beginning of Year Two, and they will be followed over 4-6 months. Comparisons will be made across cohorts/grade levels to understand the language-reading relations for DLLs at different stages of reading development. Aim 1 will examine the unique and shared contributions of oral language skills in DLLs’ two languages to their English reading scores. The language components will include metalinguistic awareness (e.g., phonological awareness), structural language skills (e.g., vocabulary) and high-level skills (e.g., listening comprehension). Aim 2 will investigate the language and reading relationship for DLLs of different levels of oral language proficiency in English and Spanish. Aim 3 will track the language- reading relations developmentally over time and across cohorts/grade levels. The proposed study will result in theoretical knowledge for second language reading models. The results will also have important implications for reading instruction, assessment and intervention for DLL children.