The authors shed light on individuals' development of the ability to use thematic and containment relations to organize concepts hierarchically. The authors used a new paradigm calling for the organization of word concepts into a containment-relation-oriented (CRO) hierarchy to collect data from 120 individuals at varied educational levels (Grade 2 to university). Findings indicate improved ability to map concepts by thematic and containment-oriented relations between Grades 2 and 4. Although there was no evidence of a developmental thematic-to-CRO shift in the organization of concepts, findings suggest that such a shift may be triggered by task-inherent properties. Evidence also strongly suggests that individuals who are otherwise unable to integrate isolated information units into complex knowledge structures may succeed when adequately assisted. The authors discuss findings in terms of their educational implications. (Contains 5 figures, 5 tables, and 2 notes.)