Scaled analog modeling ("sandbox modeling") allows deformational processes, such as the development of a mountain belt, to be observed in real time in a classroom setting. However, the actual learning gains from exposure to sandbox modeling in geology courses in higher education settings have not been explicitly studied. We begin to investigate the possible effects of incorporating a sandbox modeling activity on geologic understanding in an upper-level tectonics class. The designed activity utilized a cycle-based learning approach, where the 11 participating students predicted outcomes of different deformation experiments and then evaluated and revised their predictions in the light of their experimental observations. Scored predictive sketches and a spatial visualization test administered before and after the sandbox activity demonstrate improvements in geological understanding of deformation, the influence of different mechanical properties on deformation style, and penetrative thinking skill. The observed gains were particularly marked for students who had poorly developed penetrative thinking skills prior to the activity. These results indicate that the use of sandbox models in the classroom may have a measurable effect on penetrative thinking skills and geologic understanding, particularly in students with less expertise. However, further study is required to test if these effects can be reproduced, and shown to be statistically significant, in larger groups of students.