In this article, the author describes pre-service teachers' understandings of English language learners (ELLs) and the ways that their understandings evolved through participation in a Structured English Immersion (SEI) course. To provide the context of this study, the author begins with a brief review of recent policies in Arizona that affect the education of ELLs and the preparation of teachers who will serve them. She then reviews two areas of literature: (a) what teachers need as a means to be prepared to work with ELLs and (b) the use of reflection in teacher preparation. She follows the literature review with a brief discussion of the current tensions created by the mismatch between the literature and the Arizona mandates. In an attempt to balance these tensions, she explains how she designed her SEI course, describing her research approach and findings. In the final section of the article, she presents the implications of her findings for teacher educators, teacher preparation programs, and policy. (Contains 2 tables.)