Many educators believe that solid modeling software has made teaching two- and three-dimensional visualization skills obsolete. They claim that the visual tools built into the solid modeling software serve as a replacement for the CAD operator's personal visualization skills. They also claim that because solid modeling software can produce drawings from the solid models, teachers no longer need to teach two-dimensional drawing or two-dimensional CAD. They are wrong! To provide the best possible education, teachers do need to teach two-dimensional drawing or CAD. Creating simple solid models requires little in the way of personal visualization skills. However, as solid models grow more complex, the visualization tools built into solid modeling software can only help so much. This article discusses good personal visualization skills as a prerequisite to success with advanced solid modeling and how to develop these skills. (Contains 5 figures.)