Curriculum reform brings new approaches to classroom practice. As changes to the curriculum are implemented, teachers need to receive additional support from textbooks and other materials. In the study presented in this paper, we explored the use of resources during the process of educational reform in Croatia. The focus was on the use of a mathematics textbook set as the main resource, but the use of other material and non-material resources was also examined. The study also dealt with the social factors that influenced the use of these resources. It was designed as a case study of one mathematics teacher and her students, examined at three time points, before the reform, in the preparation period, and subsequent to the implementation of the reform. The results showed that the textbook set is a stable resource over the time periods, although it did undergo some changes towards digitalization. The teacher's professional development was shown to be an important non-material resource during the period of change. The research also revealed that the participants' decisions concerning the use of resources depended on some social issues, such as norms concerned with being a teacher or a student. The study showed that longitudinal monitoring of the use of resources in the period of curricular change may contribute to a better understanding of the processes of instructional transformation and development.