Within the study of geometry in the middle school curriculum is the natural development of students' spatial visualization, the ability to visualize two- and three-dimensional objects. The national mathematics standards call specifically for the development of such skills through hands-on experiences. A commonly accepted method is through the instruction of Origami, the art of paper folding. This study focused on Origami's impact as a teaching tool in the middle school mathematics classroom. The effects of Origami instruction on a group of seventh grade mathematics students' (n = 56) spatial visualization skills and level of geometry understanding were investigated using a pre-test/post-test quasi-experimental design. A 2 (group) x 2 (gender) factorial method was used on gathered data via three separate spatial tests (Card Rotation, Paper Folding, and Surface Development Tests) and a subset of released National Assessment of Educational Progress questions. After controlling for initial differences, an analysis of covariance revealed a significant interaction effect between group and gender for one of three spatial visualization tests. For geometry knowledge, no significant differences were found. Results imply that Origami lessons blended within mathematics instruction are as beneficial as traditional instruction in building an understanding of geometric terms and concepts, though the approach affects the spatial ability of males and females differently. (Contains 5 tables and 1 figure.)