Identity formation is a critical dimension of how and why students engage in science to varying degrees. In this paper, we use the lens of identity formation, and in particular identities in practice, to make sense of how and why Melanie, over the course of sixth grade, transformed from a marginalized member of the science class with a failing grade to a highly valued member of the sixth-grade science community with a perfect score of a 100% for the sixth-grade exit project. Our findings reveal that the different figured worlds of the science classroom, such as whole class, small group work, and individual work, offered Melanie different affordances for identity formation that were built upon across such spaces, in both productive and unproductive ways. Our findings also take up the kinds of critical roles that members of her classroom community, in particular teacher and peers, play in supporting and constraining such a transformation. We discuss the implications identity formation has for understanding issues of gender equity and science learning. (Contains 1 table and 1 figure.)