This manuscript examines how two students develop and express agency in and through high school physics. It tells the stories of two youth from a low-income, urban community to elucidate the important components of critical science agency in a physics context, and to situate a set of claims about how youth develop and express this concept. This research is part of a larger multiyear study of democratic practice in middle- and high-school science. We present three claims: (a) that critical science agency is intimately related to the leveraging and development of identity, (b) that critical science agency involves the strategic deployment of resources , and (c) that developing critical science agency is an iterative and generative process. Two university researchers have co-written this paper with the two students whose experiences serve as the cases under investigation, to provide both an "emic" perspective and student-focused voices that complement and challenge the researchers' voices.