In recent years, research on mathematics teachers' beliefs has increasingly shifted its focus toward understanding their connection with instructional practices. This article introduces a model designed to explore mathematics teachers' beliefs through a comprehensive analysis of their practices. The contributions of models that study the relationship between beliefs and practices of teachers, such as those from Schoenfeld (Journal of Mathematical Behavior, 18(3), 243-261, 2000) and Cobb and Yackel (Educational Psychologist, 31(3), 175-190, 1996), were reviewed and considered. Additionally, it includes methodological considerations from Leatham and Speer for studying beliefs. These approaches are integrated by utilizing the notions of practice, types of didactic-mathematical practices and norms, derived from the onto-semiotic approach, as the central organizing axis. Furthermore, we demonstrate the application of these stages of analysis for exploring teachers' beliefs by analyzing the beliefs of a prospective mathematics teacher. The findings enable us to identify the beliefs held by this prospective teacher regarding the use of introductory activities characterized by a high motivational level but a low mathematical level. Additionally, these results provide insights into potential avenues for developing training programs aimed at instigating a shift in these beliefs, thereby fostering an enhancement in teaching practices. These outcomes show the feasibility of the analytical model proposed in this article.