Our work on the SIOP Model started in the early 1990s when there was a growing population of multilingual learners in the United States, but no coherent model for teaching this student population. We began by reviewing the literature and examining district-produced guidelines for multilingual learners in an effort to find agreement on a definition of sheltered instruction. A preliminary observation protocol was drafted and field-tested with sheltered instruction teachers. A research project through the Center for Research on Education, Diversity, & Excellence (CREDE) enabled us to engage in an intensive refinement process and to use the SIOP Model in a sustained professional development effort with teachers on both the East and West Coasts. Through this process of classroom observation, coaching, discussion, and reflection, the instrument was refined, and it evolved into the Sheltered Instruction Observation Protocol, or as it has come to be known, SIOP"--