<![CDATA[Purpose: This study aims to explore teachers’ mathematical-technological knowledge in mathematics learning through the GeoGebra application, with a particular focus on how teachers construct, adapt, and implement this knowledge in designing instructional practices.Method: This research employed a qualitative, single-case study design. The participants consisted of eight mathematics teachers who were also graduate students. Data were collected through observations, field notes, video recordings, and weekly progress reports during an eight-week project-based learning activity involving the design of GeoGebra-based instructional materials. The data were analyzed using triangulation and coding techniques to identify patterns in how teachers integrated mathematical content and technology in their lesson designs.Findings: The findings identify two categories of teachers’ mathematical technological knowledge: moderate and expert teachers. Moderate teachers tend to use GeoGebra as a computational tool through numerical and algebraic approaches, resulting in simpler instructional designs. In contrast, expert teachers use GeoGebra dynamically for visualization, exploration of mathematical relationships, and interactive representations, leading to more complex, conceptually rich designs. These differences indicate that teachers’ technological knowledge significantly influences the quality of technology integration in mathematics learning.Significance: This study highlights the critical role of teachers’ mathematical technological knowledge in effective technology integration. It provides empirical insights into how variations in such knowledge shape instructional design and underscores the importance of professional development that integrates both technical and pedagogical competencies for meaningful mathematical representation.]]>
