This descriptive and interpretive multi-case study investigated secondary prospective teachers' (PTs') beliefs about mathematical authority and how their student teaching experience(s) influenced their beliefs. The theoretical framework guiding this study was comprised of a novel definition for mathematical authority I developed, a conception of beliefs as informing an individual's actions (Rokeach, 1968), and a theorization of how individuals hold beliefs in a system of beliefs (Green, 1971). Six PTs who student taught during the Fall 2021 semester were selected to participate in the study, four of whom are discussed in this dissertation. For each PT, data sources included three semi-structured interviews prior to student teaching, a lesson plan interview during student teaching, three semi-structured interviews after student teaching, PT generated mathematical authority diagrams prior to and after student teaching, and artifacts from their student teaching practicum (e.g., lesson plans and weekly reflections). To understand each PT's beliefs, all data was initially coded with broad codes informed by prior research on mathematics teachers' beliefs and my theoretical framework. Through an iterative process of coding and employing the constant comparative method (Strauss & Corbin, 1998), new codes emerged and the coding scheme was refined. Coded data informed my written narratives of each PT's beliefs, which are presented as the results of this study. The participating PTs believed numerous sources can be mathematical authorities in the classroom, but they mainly focused on the teacher and students as mathematical authorities. The PTs had varying beliefs about the teacher and students as mathematical authorities, but across the four PTs, each believed the teacher is the main mathematical authority in the classroom and believed all students can be mathematical authorities. Conducting a cross-case analysis of the PTs' belief systems enabled me to make inferences for differences in what each PT believed, particularly their beliefs about students as mathematical authorities. Student teaching seemed to reinforce the beliefs of each PT and provided a continued context for each PT to develop a pedagogy informed by their beliefs. Implications for mathematics teachers, mathematics teacher educators, and mathematics education researchers are discussed. [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.]