Preservice science teachers face numerous challenges in understanding and teaching science as inquiry. Over the course of their teacher education program, they are expected to move from veteran science students with little experience learning their discipline through inquiry instruction to beginning science teachers adept at implementing inquiry in their own classrooms. In this study, we used Aikenhead's ("Sci Educ" 81: 217-238, 1997, "Science Educ" 85:180-188, 2001) notion of border crossing to describe this transition preservice teachers must make from science student to science teacher. We examined what one cohort of eight preservice secondary science teachers said, did, and wrote as they both conducted a two-part inquiry investigation and designed an inquiry lesson plan. We conducted two types of qualitative analyses. One, we drew from Costa ("Sci Educ" 79: 313-333, 1995) to group our preservice teacher participants into one of four types of potential science teachers. Two, we identified successes and struggles in preservice teachers' attempts to negotiate the cultural border between veteran student and beginning teacher. In our implications, we argue that preservice teachers could benefit from explicit opportunities to navigate the border between learning and teaching science; such opportunities could deepen their conceptions of inquiry beyond those exclusively fashioned as either student or teacher.