This dissertation is a linguistic ethnography of a high school Astronomy/Oceanography classroom in southern Arizona, where an exceptionally promising, novice, white science teacher and mostly Mexican-American students confronted issues of identity and difference through interactions both related and unrelated to science learning. Through close analysis of video-recorded, naturally-occurring interaction and rich ethnographic description, the study documents how a teacher and students accomplished everyday classroom life, built caring relationships, and pursued scientific inquiry at a time and in a place where nationally- and locally-circulating discourses about immigration and race infused even routine interactions with tension and uncertainty. In their talk, students appropriated elements of racializing discourses, but also used language creatively to "speak back" to commonsense notions about Mexicanness. Careful examination of science-related interactions reveals the participants' negotiation of multiple, intersecting forms of citizenship (i.e., cultural and scientific citizenship) in the classroom, through multidirectional processes of language socialization in which students and the teacher regularly exchanged expert and novice roles. This study offers insight into the continuing relevance of racial, cultural, and linguistic identity to students' experiences of schooling, and sheds new light on classroom discourse, teacher-student relationships, and dimensions of citizenship in science learning, with important implications for teacher preparation and practice. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]