This paper describes an instructional approach for language minority students in high school science and social studies--using explanatory models or graphical representations of disciplinary concepts to guide students systematically as they construct a concept or conceptual relationship. Data came from a longitudinal study of two successive groups of Mexican American high school students in Chicago who were attending a weekly outreach program to enhance their academic skills for college. As the first group was studied and their learning strategies became more apparent, a method for expanding those strategies and energizing more active use of everyday concepts and language was refined for use with the second group. A preliminary analysis of observations indicated that students were hindered in learning complex concepts because the strategies and skills they possessed were too limited. At the same time, students brought many social skills to classroom interaction, indicating their high motivation. After much reflection and experimentation, teachers realized that literacy experience in one or both languages prepares students to use language for learning. Teachers could then focus on using explanatory models to present content and influence learning without requiring a mediating academic language. This experience led to the conclusion that substituting language arts instruction for appropriate high school content is unacceptable educational policy because it closes the door to higher learning. (Contains 25 references.) (ND)