This dissertation studies students' identity negotiation in a project-based Advanced Placement (AP) Environmental Science class. The College Board has encouraged schools to diversify enrollment in AP STEM (Science, Technology, Engineering, and Math) courses, in which White and Asian males have been historically overrepresented. This trend may be connected to the ways in which underrepresented students socially identify with this learning context. Project Based Learning (PBL) has the potential to support students' connection with AP STEM coursework by tasking them with solving real-world problems by using discipline-specific skills and practices. This mixed-methods study uses situative theories of identity to analyze the opportunities and constraints to students' identities in the context of a PBL AP Environmental Science course offered in an urban, poverty-impacted school district. Findings from this study highlight the different ways that AP and Science identities can manifest, and suggest a relationship between perceived agency in the class and certain students' future plans to pursue science majors in college. In studying the identity processes involved in this evolving context, I hope to shed light on ways that increasingly diverse groups of students might socially identify with the domains of AP and Science. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]