Tangible user interfaces (TUIs) have been the focus of much attention in the HCI and learning communities because of their many potential benefits for learning. However, there have recently been debates about whether TUIs can actually increase learning outcomes and if so, under which conditions. In this article, we investigate the effect of object representation (physical vs. virtual) on learning in the domain of spatial skills. We ran a comparative study with 46 participants to measure the effects of the object representation on the ability to establish a link between 2D and 3D representations of an object. The participants were split into two conditions: in the first one, the 3D representation of the object was virtual; in the second one, it was tangible. Findings show that in both conditions the TUI led to a significant improvement of the spatial skills. The learning outcomes were not different between the two conditions, but the performance during the activities was significantly higher when using the tangible representation as opposed to the virtual one, and even more so in for difficult cases.