The purpose of this case study was to better understand the nature of the experiences of a preservice teacher, self-identified as having mathematics anxiety as she planned and implemented instruction during her internship by answering: What is the nature of the experiences of a preservice teacher, self-identified as having mathematics anxiety, as she planned for mathematics instruction during her final internship? What is the nature of the experiences of a preservice teacher, self-identified as having mathematics anxiety, as she implemented mathematics instruction during her final internship? Using an interpretivist approach to a case study inquiry, I used semi-structured interviews, observations, audio journals, and artifacts to collect data on a preservice teacher, cooperating teacher, and college supervisor. Member checking was used with interview data and a peer reviewer reviewed all data collection and analytic procedures. I analyzed the data using content and thematic analysis. The findings indicated that lack of planning, lack of instructional support, lack of content knowledge, and lack of transfer of what she learned in the mathematics methods course impacted the preservice teacher’s planning and implementation of mathematics instruction. In this way, the study identified the importance of instructional support for preservice teachers during K-12 classroom experiences, theory-to-practice connections between coursework and field experiences, and preservice teacher reflection to recognize weaknesses and seek out solutions to solve problems of practice. The study closed with a discussion from the viewpoint of reviewed literature, my interpretation of the findings and suggestions for future research.