This study, conducted from a constructivist perspective, examined the belief system of a prospective elementary teacher (Barbara) about science teaching and learning as she developed professional knowledge within the context of reflective science teacher education. From an analysis of interviews, observation, and written documents, I constructed a profile of Barbara's beliefs that consisted of three foundational and three dualistic beliefs. Her foundational beliefs concerned (a) the value of science and science teaching, (b) the nature of scientific concepts and goals of science instruction, and (c) control in the science classroom. Barbara held dualistic beliefs about (a) how children learn science, (b) the science students' role, and (c) the science teacher's role. Her dualistic beliefs formed two contradictory nests of beliefs. One nest, grounded in lifelong science learner experiences, reflected a didactic teaching orientation and predominantly guided her practice. The second nest, not well grounded in experience, embraced a hands-on approach and predominantly guided her vision of practice. The findings accentuate the complexity and nestedness of teachers' belief systems and underscore the significance of identifying prospective teachers' beliefs, espoused and enacted, for designing teacher preparation programs. (Contains 2 tables and 1 figure.)