Recent science educational policy reform efforts call for a shift toward practice-focused instruction in kindergarten–Grade 12 science education. We argue that this focus on engaging students in epistemic practices of science opens up new possibilities for the design of learning environments that support the stabilization of learners’ science-linked identities. Learning environments often assume that youth come to them without relevant identity resources to contribute or that the learning environment has no bearing on the disciplinary identification of individuals. We conducted this research while developing a year-long course to teach high school biology by engaging youth in interest-driven projects focused on contemporary topics. We explored how engaging youth in the epistemic practices of science in culturally expansive ways supported their science-linked identification. We propose a model grounded in social practice theory that describes aspects of students’ stabilization of disciplinary identities. We found that (a) deepening participation in scientific practices is linked to whether or not youth have opportunities to coordinate their engagement with their existing identities; and (b) material, relational, and ideational identity resources and qualities of the learning environment mediate how youth stabilize disciplinary identities in interactional moments.