Furniture carpentry uses spatial structure and geometry, e.g. mortise-tenon joints, which require cognitive judgments of hidden views and spatial understanding. For the furniture carpentry novice, the idea of spatial geometry in the mortise-tenon joint is difficult to understand because furniture carpentry drawings are usually two-dimensional (2-D) graphics. A great deal of cognitive effort and furniture design drawing practice is required to accurately visualize these 2-D objects as three-dimensional (3-D). Novices unfamiliar with 3-D spatial concepts often make mortise-tenon joint errors when making furniture. Augmented reality (AR) has helped train carpentry novices to understand the conceptual manifestations of 3-D space. In this study, we recruited 40 freshmen for a basic general carpentry class with an Experimental (n = 20) and a Control (n = 20) group. Both groups were asked to make, using their hands and a wood saw, mortise-tenon joints at three levels of difficulty: preliminary, mid-level, and advanced. The Experimental group was given AR training; the Control group was not. After the three phases had been completed, we found that the AR training helped Experimental group students improve their 3-D visualization and indirectly improved their grasp of furniture carpentry skills and of the complicated mortise-tenon joint structure.