Within the last 30 years, geographical information systems (GIS) have been used increasingly in the training of geographers. On the basis of the philosophy of technology and instrumental genesis, we sketch how the use of instruments interacts with learning processes and outline how this can be studied. We empirically analyse students' learning processes and the influences of teaching practice in an introductory course in GIS. We show that students have different strategies for creating their personal instrument for spatial thinking and how teaching interacts with the students' learning processes. Finally, we discuss how GIS may gradually alter future professional development of geographers. (Contains 4 figures.)