This researcher investigated the relationship of hierarchical classification processes in subjects categorized as to developmental level as defined by Piaget's theory, and explored the validity of the hierarchical model and test used in the study. A hierarchical classification test and a battery of four Piaget-type tasks were administered individually to a group of 60 randomly-selected high school students and to a group of 52 randomly-selected junior high school students. Students in each group were categorized as concrete, transitional, or formal by determining their performance on the battery of four Piaget-type tasks in science. In addition to the Piaget-type tasks, a hierarchical classification test was administered to each individual within each group. The test consisted of a six-level hierarchy called a Natural Things Test. Results supported the assumption that students capable of forming and manipulating symbolic representations of experience (Formal Operations) would experience little difficulty on the hierarchical test. The assumption that students dependent upon concrete cues would experience difficulty on the hierarchical test was not as clearly supported. (Author/HM)