In an ethnographic study of one high school mathematics department made up of four African American teachers, I explored their co-construction of knowledge about teaching mathematics for social justice. This began with an in-depth study of each teacher's professional identity, their emotional connections to teaching in their local African American community, and their actions in the classroom. My overarching analysis of one school year with this department was centered around the teachers' weekly department meetings, in which they worked together to construct project-based, justice-focused mathematics units for their high school students. Given that these teachers had all grown up locally and that their student body was 99% Black, the teachers identified strongly with their students' racial and local identities. However, the teachers' diverse driving concerns and vision for teaching led to lively and in-depth discussions about what teaching mathematics for justice truly meant and how project-based learning might further their goals for their students' mathematical and holistic learning. The teachers identified several ways in which project-based learning aligned with their individual and corporate vision for high-quality, meaningful, and antiracist mathematics teaching for their students. They did this by analyzing the particulars of their students' struggles and needs, in conjunction with their own knowledge about what lay ahead for students--both in terms of future demands for mathematical knowledge and, more broadly, the realities of adult life for Black Americans in their city. The teachers also identified obstacles they faced in trying to plan for and implement project-based mathematics units. They were expected to help their students master an unrealistic number of mathematics standards in a limited amount of class time, under the ever-present threat of standardized tests which could bar their students' entry into college and careers. The teachers found they had no exemplars to follow in navigating coverage of these specific standards via mathematics projects. In addition, they had difficulty connecting the content standards for high school mathematics to the kinds of real-life contexts best suited to project-based learning. As the year unfolded, the teachers circumvented some of these obstacles by finding pockets of time around the edges of the standardized testing regime and by identifying a few mathematics and statistics topics that they were able to develop into meaningful projects and project-like lessons. However, the teachers' learning took another turn as well. Together, they generated systemic critiques of U.S. high school mathematics education and the politics of schooling, pointing out specific funding policies that had stymied their efforts. They also identified gaps in their own teacher training and professional learning that would need to be filled to equip them to implement justice-focused, project-based pedagogy. I argue that, even while funding issues continue to plague schools like Maplewood, these concerns may obscure other real issues around high school mathematics teacher learning and practice. Math teachers who want to implement project-based pedagogy need specialized support to flesh out this vision, integrate it with their concerns about standardized testing, and put it into practice. Those concerned with teacher professional learning, both pre-service and in-service, could contribute to the development of project-based learning strategies by co-constructing this vision with teachers, meeting their felt need to understand real-world connections to the high school mathematics standards, and providing them with curriculum materials suitable for project-based pedagogy. [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://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]