We use identity as a multidimensional lens to explore ways in which beginning teachers saw themselves as scientists and as science teachers during and after 10-week summer apprenticeships at a science lab. Data included four interviews with each teacher, three during the apprenticeship and one after the first year of teaching. Two themes emerged that were used to organize the findings: (a) science as a practice and (b) science as a community of practice. Teachers came to appreciate certain science practices, speech acts, and tools. As scientists, they noticed and engaged in the nonlinearity, messiness, risk taking, evolution over time, and complexity of science (their own and others'), and in both levels of scientific activity, theory and data, and their interplay. Their scientist identity also came to incorporate the delicate dynamics of collaboration, autonomy, and mentoring within a community. However, for several reasons the teachers raised, such practices became elements of their science teacher identities to differing degrees. What they experienced as science teachers was a sense of conflict. At times this conflict took the form of ambivalence, a back-and-forth movement between their sense of the practice of science and their sense of what makes school different from the lab. © 2005 Wiley Periodicals, Inc. Sci Ed, 89:492–516, 2005