Defines spatial structuring as the mental operation of constructing an organization or form for an object/set of objects. Examines in detail students' structuring and enumeration of two-dimensional rectangular arrays of squares. Concludes that many students do not see row-by-column structure. Describes various levels of sophistication in students' structuring of arrays, and elaborates on the nature of mental process of structuring. Contains 16 references. (Author/ASK)