In this chapter we present data regarding the validity and reliability of the TOSA, including how children responded differently to the test from age 3 to 4. We also discuss findings from the 2-D and 3-D trials that, combined, generated the overall TOSA scores. The dimensional scoring schemes used were intended to allow children to receive partial credit for displaying some knowledge of how to reproduce the models for the respective trials. At the beginning of this chapter we present some exploratory and descriptive analyses of the test items and performance on the scoring dimensions. These are intended to help understand, at a high level, the specific errors children make, which aspects of the tasks were easy or difficult, and the properties of the models that appear to have modulated the challenge. These explorations are included to contribute to the development of new research questions and explore strengths and weaknesses in preschoolers' spatial skills. (author abstract)