A project to develop an explicit model of sheltered instruction that teachers can use to improve the academic success of their limited-English-proficient (LEP) students is described, focusing on the development of an observation tool for use in the study. The Sheltered Instruction Observation Protocol (SIOP) provides concrete examples of the features of sheltered instruction that can enhance and expand teachers' instructional practice. In this project, the model was used to train middle school teachers to implement effective sheltered strategies in four large urban school districts. Project teachers used sheltered instruction in a variety of settings, including traditional English-as-a-Second-Language (ESL) classes, content-based ESL classes, and sheltered content classes. The report describes the project and summarizes results. The lesson plan checklist from the SIOP is appended. Contains 15 references. (MSE)