Learning to reason spatially is increasingly recognized as an essential component of geometry education. Generally taken to be the "ability to represent, generate, transform, communicate, document, and reflect on visual information," "spatial reasoning" uses the spatial relationships between objects to form ideas. Spatial thinking takes a variety of forms, including building and manipulating two- and three-dimensional objects; perceiving an object from different perspectives; and using diagrams, drawings, graphs, models, and other concrete means to explore, investigate, and understand abstract concepts such as algebraic formulas or models of the physical world. Despite the overwhelming support for spatial thinking as a worthwhile educational activity, tensions within the school curriculum have resulted in downplaying geometry and elevating either numeracy (primary level) or algebra (secondary level). The author's work with recent high school graduates in college-level mathematics and mathematics teaching classes has shown that their understanding of geometric concepts is mainly algebraic or numerical, not spatial. As a result, the author has explored the effectiveness of different learning tasks and teaching strategies to develop the spatial side of students' geometric understanding. This article describes the three strategies (experiential, inductive, comparative) and the five learning tasks that she has found most effective for deepening the spatial aspect of students' geometric understanding. (Contains 6 figures.)