In modern information societies, evaluating information, data, or knowledge claims is crucial. As these activities are influenced by epistemological beliefs, such beliefs are a key element of education in the sense that educational institutions intend to prepare students for professional and social life. Hence, this study aims to examine the development of students' epistemological beliefs about mathematics in the course of studying mathematics at university level. In a sequential cohort study, 1774 responses of mathematics students were surveyed in three consecutive years. The participants rated claims about the nature of mathematical knowledge in a spontaneous manner - a research procedure stimulating their connotative aspects of epistemological beliefs. Analyses showed that students hold different epistemological beliefs regarding 'mathematics as a scientific discipline' and 'mathematics as a school subject' -- with mathematics major students and future upper secondary school teachers rating 'mathematics as a school subject' to be relatively simple and superficial compared to future primary school and lower secondary school teachers. Nonetheless, all student groups find 'mathematics as a scientific discipline' to be significantly more complex and profound than 'mathematics as a school subject'. Interestingly, the domain-specific beliefs remain rather stable in the course of studies regardless of the students' study programme.