Spatial ability tasks appear on many intelligence and aptitude tests. Although the construct validity of spatial ability tests has often been studied through traditional correlational methods, such as factor analysis, less is known about the cognitive processes involved in solving test items. This study examines the cognitive processes involved in the assembling objects task found on the Revised Minnesota Paper Form Board Test (RMPFBT), a spatial task in which a test taker must mentally assemble two-dimensional objects. A two-part study was conducted to examine the construct validity of these items and to explain how test takers solve assembling objects tasks. The first part of the study used quantitative methods to examine the contribution of item characteristics to the difficulty of the item and the response time necessary to solve the item. The second part of the study utilized an eye-tracking device to qualitatively examine the steps examinees follow to solve these items. As a result of the second part of this study, a new cognitive processing model is proposed. (Contains 3 figures and 6 tables.)