Background/Context: While different instructional approaches have been proposed to integrate academic content and English proficiency for English language learning (ELL) students, studies examining the magnitude of the relationship are non-existent. This study examined the relationship between the "form" (i.e., conventions, organization, and style/voice) and "content" (i.e., specific knowledge and understanding of science) of expository science writing among third grade ELL students in the beginning and at the end of each year during the three-year implementation of the intervention. Purpose/Objective/Research Question/Focus of Study: The study is part of a larger five-year research and development project aimed at improving science and literacy achievement of ELL students in urban elementary schools in a large school district. Research Design: The intervention was comprised of curriculum units for students and teachers and professional development workshops for teachers throughout the school year. As a school-wide initiative, all third grade teachers and their students from six treatment schools participated. The study involved 683 third graders during the first year, 661 third graders during the second year, and 676 third graders during the third year. Approximately half of the students were Hispanic and the other half were Black, including Haitians and Caribbean Islanders. A writing sample was used as a measure of English proficiency and ability to explain science concepts in writing. At the beginning and end of each school year, teachers administered the writing prompt to their students. Data were analyzed using a hierarchical linear modeling approach. Findings/Results: The results indicated significant relationships between writing form and content at both pretest and posttest, with a stronger relationship at posttest. The effect of English proficiency on the magnitude of the relationship was significant only at posttest, for which the relationship was stronger for non-ELL students. The results suggest that through our intervention over the course of the school year, students with greater English proficiency learned science content and developed English literacy simultaneously, whereas students with lower English proficiency did not show this simultaneous growth to the same degree. Conclusions: Thus, interventions such as ours, which primarily present science curriculum and instruction in English, might be expected to have limited positive effects for ELL students at the beginning and intermediate levels of English proficiency. The results point out potential conflicts in current educational policies, including high-stakes testing and accountability and English-only policies, which affect ELL students.