The authors examined a model of instruction for English-language learners (ELLs) who were learning academic English while they tried to meet content standards required by the nation's education reform movement. In previous work (J. Echevarria, M. E. Vogt, & D. Short, 2000), the authors developed and validated a model of instruction (Sheltered Instruction Observation Protocol; SIOP model) for ELLs. In this study, the authors tested the model for its effects on student achievement. Findings revealed that students whose teachers implemented the SIOP model performed slightly better than did a comparison group on an expository essay writing task, which closely approximated academic assignments that ELLs must perform in standards-based classrooms. (Contains 2 figures and 7 tables.)