This paper presents findings from a study of kindergarteners’ understandings of spatial decomposition. Although the term “composition/decomposition” frequently appears in the spatial thinking literature, studies on spatial decomposition are lacking. The purpose of this study was to begin to address the gap in the literature by building an understanding of what children understand, in a particular virtual context, about spatial decomposition, and how they construct these understandings. The significance is threefold: first, the topic itself is vital, in that part/whole relationships pervade our existence as humans; second, the topic is well situated within an ongoing, world-wide research agenda on children’s mathematical, geometric, and spatial thinking; and third, this study extends learning theory in the area of virtual learning, a nascent area in need of refinement. The theoretical framework was an emergent interactionist approach that recognized the interconnectedness of the psychological, the biological, and the sociological. The methodology included inductive, qualitative methods, consistent with the epistemological and theoretical foundations of this study. Document analysis and case study were co-employed to analyze the preserved words, actions, and work products of a group of 20 kindergarten children as they engaged in solving puzzles requiring spatial decomposition. Data were analyzed via coding, descriptive and abstract categorizing, and theoretical memoing, resulting in the following claim: The children showed evidence, from what they said and did, of certain understandings of the whole and its parts, and of a fluid, working understanding of some relationships between the whole and its parts, in the context of spatial decomposition activities in a graphical software environment. Within the affordances and constraints of this software, these children moved fluidly and easily between wholes and parts, between holistic and analytic thinking, between the conceptual and the procedural, and between the concrete and the imagistic, suggesting that virtual environments such as that employed may be particularly suited to children’s ways of thinking.