This article is a case study of a second-year middle school science teacher's beliefs about science and science teaching and how these beliefs influenced—or failed to influence—classroom instruction. It illustrates how beginning teachers struggle to reconcile (a) conflicting beliefs about what is desirable, and (b) conflicts between what they believe is desirable and what is possible within the constraints of their preparation and the institutions in which they work. This teacher, for example, struggled to reconcile his view of science as a creative endeavor with his belief that students need to be provided with a high degree of structure in order to learn within the context of formal schooling. He also had difficulty resolving the conflict between the informal (“messing about”) type of science learning that he believed was desirable and the personal and institutional constraints he faced in the classroom.