When students classify, they embark on observing and identifying the properties of the object, and then they categorize, sort, group, organize, arrange, or grade objects into smaller and similar clusters or divisions. Therefore, observing and classifying are fundamental skills for comparing and contrasting material objects. In addition, observing and classifying are skill-based stepping stones to helping students to think spatially. The following discussion focuses on three questions: (1) What is spatial thinking? (2) How do spatial-thinking skills apply to everyday problems and situations? and (3) How do spatial-thinking skills integrate into the science curriculum?