This dissertation contains three articles accompanied by an introduction and conclusion chapter. The first article, Chapter Two: Middle School Learners Ontological Trying-on of Dimensions: A Phenomenological Investigation, details a post-intentional phenomenological research study with 5th and 6th grade learners and serves as the pilot study connecting the three articles. The second article, Chapter Three: The Embodiment of Cases as Alternative Perspective in a Middle School Geometry Hypermedia Site, provides the theoretical and design framework guiding the design of a hypermedia site used with learners in a second iteration of the design-based research agenda with Space and Perspective. The third article, Chapter Four: Productive Problematization: Moments When Perspectives Shift in Middle School Mathematics, presents findings from a post-intentional phenomenological study with 21 eight-grade learners investigating Space and Perspective with the hypermedia site. The study aimed to understand what it is like for learners to experience a shift in perspective.