This report presents the results of a study designed to evaluate the Johnson O'Connor Research Foundation's (JOCRF's) measurement of structural visualization. Three experimental tests--the Incomplete Open Cubes Test, the Guilford-Zimmerman Spatial Visualization Test, and Raven's Advanced Progressive Matrices--were added to the JOCRF's test battery and administered to between 2,199 and 2,814 clients using the JOCRF's aptitude testing services. Complete measurements were available for 917 males and 801 females. Tests from the regular battery also analyzed were: (1) measures of structural visualization, the Wiggly Block and Paper Folding Tests; (2) Analytical Reasoning; and (3) Inductive Reasoning. Scores from item response theory methods were measured for the tests. Results suggest that: the Wiggly Block Test contains a small non-spatial component, attributable to the use of a distinctive feature-extraction strategy; and the Paper Folding Test contains a large non-spatial component, attributable to the use of a distinctive feature-extraction strategy and general reasoning ability. Overall, the results show that the relative independence of spatial measures from verbal and reasoning measures is no longer characteristic of many spatial tests currently in use. Ten figures and 17 tables summarize study data. A 65-item list of references is included. (SLD)