In this article we examine the scientific identity formation of two young women of color who attend an urban vocational high school. One young woman lives in an urban setting, while the other lives in a suburban setting. We describe how these young women's identities influence and respond to experiences in school science. In particular, we describe how the experience of marginalization can make membership in a school science community impossible or undesirable. We also describe the advantages that accrue to students who fit well with the ideal identities of an urban school. Finally, we describe some of the difficulties students face who aspire to scientific or technological competence yet do not desire to take on aspects of the identities associated with membership in school science communities. © 2001 John Wiley & Sons, Inc. J Res Sci Teach 38: 965–980, 2001