In this article we report findings from research through the Center for Research on the Educational Achievement and Teaching of English Language Learners (CREATE), a National Research and Development Center. In our study we examined the efficacy of a model of instruction for English learners, the Sheltered Instruction Observation Protocol (SIOP) Model, in one content area, science. Assessments measured the acquisition of academic language and science concepts among English learners, former English learners, and English Only students in middle school science classrooms. Results indicated that students in the SIOP group performed better than controls, although not to a significant degree. Reasons for these findings are explored. Due to differential attrition of schools in the control group, caution must be used in interpreting the study's findings. (Contains 6 tables.)