In two experiments, we investigated the development of cross-sectioning ability using either three-dimensional (3D) or two-dimensional (2D) stimuli. Three to 9 year old children visualized cross-sections of either real 3D geometric shapes (Experiment 1) or 2D photographs of the shapes (Experiment 2). Performance on the 3D task was also analyzed to determine to what extent cross-sectioning ability is related to performance on more widely used spatial tasks including mental rotation and the water-level task. We found that performance on the cross-sectioning and mental rotation tasks were significantly correlated, and the 2D and 3D tasks were both successful in assessing cross-sectioning ability in young children. As expected, we also found a significant increase in cross-sectioning performance across age groups.