This study explores student agency in the context of a culturally authentic computer science (CS) curriculum implemented in an introductory CS course in two high schools. Drawing on focus group and interview data, the study utilizes qualitative research methods to examine how students exercise critical agency as they engage in the course and how the curriculum supports student agency. Findings suggest three ways in which the curriculum served as a context for student agency: (1) gaining CS knowledge and skills that students then apply to address real-world needs and problems, (2) creating opportunities to "try-on" or improvise new identities and/or envision "future selves" in CS, and (3) engaging in personally relevant project work that leverages assets students brought to their experience with the curriculum. Implications for CS education research and practice are discussed.