To achieve ambitious and equitable mathematics education, districts will likely have to extend their efforts beyond the bounds of classroom teaching and learning, and also address the social and political aspects involved in improving mathematics education. However, the literature has yet to explore the underlying boundaries that determine which policies are relevant (or not) to mathematics education, or how the subject-matter acts as a context for such framing. To that end, I conducted a comparative case study of two Missouri school districts through interviews with district leaders, observations of policymaking, and collection of relevant artifacts. Findings revealed that districts' policy boundaries were shaped by the dominant mathematics-related discourses circulating in the district and its local community, including accountability discourses and epistemological discourses about the subject. Discourses related to equity and mathematics pedagogy were less dominant and more contested, and also less influential in shaping boundary framing. Boundary framing was also mediated by factors related to the districts' organizational structures, including the size and segmentation of the central office. Though there was some attention to access and achievement in inquiry-oriented mathematics instruction at one district, both districts' boundaries around policy for mathematics education were primarily constrained to issues of achievement. Subject-neutral policies specifically addressing instructional issues were sometimes implemented in mathematics-specific ways, but other subject-neutral policies--including equity-minded efforts--never crossed into mathematics. Among other implications, these findings suggest that educational leaders, policymakers, and researchers interested in reshaping districts' policy boundaries should attend to the ways the subject-matter interacts with policies--even seemingly subject-neutral ones--to shape policy enactment and constrain improvement efforts. [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.]