A modified form of Sigel's Styles of Categorization Test was constructed, permitting the independent measurement of Descriptive Part-Whole (DPW), Relational-Contextual (RC), and Categorical-Inferential (CI) categorizations. The test was administered to 243 5th, 8th, and 11th graders on two occasions. At each grade level, a majority of categorizations were CI in nature, followed by a lower frequency of DPW responses, and a minimal frequency of RC responses. DPW responses of boys exceeded those of girls, and categorization modes were independent of intelligence. Reliable individual preferences for one or more categorization modes were obtained, as well as substantial individual differences in such preferences. Results were discussed in terms of hierarchical cognitive stage theory and a conceptual orientation shift hypothesis. (Author/JMB)