This report is one of a series of four reports examining the education of English language learners in mainstream classes. The purpose of this report is to heighten the awareness of teachers and teacher educators about issues concerning the achievement of second-level English language learners in mainstream science classrooms. Information was gathered through a review of the literature concerning teaching English language learners, site visits to a suburban high school that had implemented a team approach for working with English language learners, and through interviews with members of the teacher preparation faculty at The George Washington University. The report offers vignettes and guidelines for effective instruction, including scientific inquiry, teaching the language of science, problem solving instruction, assessment, and teacher preparation suggestions. It concludes that the goals of new rigorous science standards can only be met if mainstream teachers have knowledge and skills in how to teach the increasingly diverse student population. The recommendation is that teacher preparation programs should more required classes in culture and linguistics.