Using multiple theoretical frameworks, reflective writings and interviews, this study explores preservice elementary teachers' emerging identities as science teachers and how this identity is connected to notions of critical agency and a stance toward social justice. The study addresses two central questions pertaining to preservice teachers' conceptions as "agents of change" and how their perceptions as change agents frame their science teacher identities and understanding of teaching science in urban elementary classrooms. Their identity in the moment as elementary preservice teachers--not yet teachers--influences how they view themselves as teachers and how much agency or power they feel they have as agents of change in science classrooms. Findings suggest that science teacher education must play a more immediate, fundamental and emancipatory role in preparing preservice teachers in developing science teacher identities and a stance toward social justice.