The use by 254 Canadian children of the dimensions of gender, language/ethnicity, and body type as bases of categorization was examined. A developmental approach was taken to see whether a sequence exists in the relative predominance of these dimensions; to examine the relation between the salience of these dimensions and cognitive developmental skills; and to assess the relation between dimensional salience and the acquisition of related stereotypes during middle childhood. Findings indicated that tendencies to classify by gender and body type were strongest in kindergarten, declining significantly between kindergarten and grade 2, and again between grades 1 and 5. In contrast, categorization by ethnic group remained constant between grades K and 6. Accuracy on conservation tasks, and knowledge of gender and overweight stereotypes increased from kindergarten to grade 1, the time at which categorization by these dimensions was strongest. It is concluded that these results support the hypothesis that children use categorization by social dimensions to acquire knowledge about the associated roles in their culture. Once these roles are acquired, the child may turn to new, not yet "mastered" dimensions as the dominant basis for classification. Gender and body type matches may decline as children become less focused on external, physical attributes, while ethnicity, perhaps perceived as a complex internal attribute, remains more predominant as a basis for classification. (RH)