The ways in which mentor teachers, as school-based mathematics teacher educators, support prospective teachers during the student teaching experience of teacher preparation has been largely unexplored. In the limited instances when the work of mentor teachers has been researched, the focus ignores the various approaches mentor teachers employ to support prospective teachers' development as educators working for social and racial justice. Due to this gap, the field has not theorized nor documented the ways in which mentor teachers, who are already working for racial justice in their classrooms, can support prospective teachers to develop these skills and dispositions. Developing these skills and dispositions involves creating space for prospective teachers to evaluate their own beliefs, engage in dialogue that challenges what is considered normal in society, and examine how classrooms further marginalize students. Through developing these skills and dispositions, prospective teachers develop critical consciousness. In this dissertation study, I propose that mentor teachers are key to the development and support of preservice teachers' critical consciousness in mathematics, a subject that has been historically used to gate keep and justify racial hierarchies. This dissertation is grounded in praxis-oriented research (Lather, 1986) with the goal of theorizing and documenting mentoring for critical consciousness in mathematics teacher education. Theoretically, I build a case for the role of mentoring for critical consciousness as a way to disrupt the exclusionary forces in mathematics education by drawing on the work of educative mentoring (Feimen-Nemser, 1998; 2001) and critical mathematics consciousness (Kokka, 2020). Bringing together these two constructs, I propose the construct of "critically conscious mathematics mentoring" as a way for mathematics teacher educators to identify and document the essential elements of the practice of mentoring for critical consciousness. Empirically, this study then seeks to amplify the perspectives of mentor teachers and how they describe critically conscious mathematics mentoring as a way to disrupt the exclusionary practices in mathematics classrooms. Finally, the empirical aspects of the study are used to refine the theorization of critically conscious mathematics mentoring. This work contributes to the field of mathematics teacher education in two distinct ways. First, this study provides a new theoretical lens to examine mathematics mentor teachers' practices. Second, it illuminates the various approaches mathematics mentor teachers in diverse schools describe employing in their role in the work of preparing future teachers to enact justice-oriented pedagogies. [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.]