Theoretical frameworks for mathematics teaching and learning technology-supported provide a systematic structure in examining the contribution of the tool to conceptual development. This study examines the processes for the use of spreadsheets and the mathematical development of the participants in the tasks for performing the conversions between number systems using the instrumental genesis approach, which deals with transforming a tool into an instrument that will contribute to the conceptual development. In the study, the screen images of the worksheets of the participants, who are at the Department of Computer Technologies Program in a vocational school in Turkey, are analyzed together with the observation notes and evaluation scales prepared based on the outcomes. In the study, while the efforts of the participants to transform the spreadsheet into an instrument are observed, it is seen that their habits of paper-and-pencil experiences and misconceptions lead to an obstacle to transferring their operations to the spreadsheet and hesitations. However, their developments in instrumentalization processes are reflected by the following: they use subjective usage schemes, realize the advantages of spreadsheet functions and features, and create dynamic worksheets through dragging and cell addresses. Nevertheless, it can be stated that the reflections of instrumentalization progress on the instrumentation processes for conceptual development are limited.