The purpose of this study was to gain insights into how a PreK teacher's beliefs on readiness shaped how she adopted/adapted to a new practice that was intended to provide responsive mathematics education. To explore these issues, I constructed one descriptive case study of a teacher's beliefs and practice based on data from a broader research project. Marley, this study's focus, participated in a two-year-professional development (PD), which focused on culturally and developmentally responsive early mathematics pedagogy by connecting funds of knowledge (FoK), early mathematics teaching, and early childhood curriculum. The following questions guided my study: "How were a community-based PreK teacher's readiness beliefs related to her mathematics engagement in a play-based classroom? And how were they related to her use of children's FoK when teaching mathematics?" I analyzed qualitative data, such as interview transcripts, observational field notes, PD discussion transcripts, and teacher created artifacts, that were gathered as part of the larger research project to examine the role Marley's beliefs played in her practice. Findings highlighted that dominant within Marley's ideas and practices are understandings based on environmentalist notions of readiness. Marley's goal was to prepare children to be "good little school citizens" who can act and interact according to typical kindergarten norms. Within the environmentalist frame, "readiness" is emphasized as a mechanism that provides children with the skills, knowledge, and experiences that are considered to be needed to be ready for kindergarten schooling. Consequently, Marley's strategy for PreK teaching was to use prescriptive teaching methods, which limited pedagogical interactions between the teachers and children. How Marley took up PD contents including play-based pedagogy and incorporating children's FoK when teaching mathematics were closely linked with her environmentalist notions of readiness. Furthermore, Marley's readiness beliefs were related to types of FoK Marley noticed and chose to incorporate. Marley used FoK as a tool supporting her view of kindergarten readiness rather than a transformative approach in which the child's present home practices became the site of knowledge production that teachers learned from. Marley's notions of culture and FoK also played a role in how she incorporated children's FoK. [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.]