The Conceptual Learning and Development (CLD) Model specifies four levels of concept attainment (concrete, identity, classificatory, and formal) and three uses of concepts (problem solving, subordinate-supraordinate, and principles). Longitudinal and cross-sectional studies of concept attainment may be conducted. The results of this study of 300 children in grades two, five, eight, and eleven, are discussed. Each child's level of attainment and use of four different concepts--equilateral triangle, cutting tool, noun, and tree-were assessed. Three hypotheses based upon the CLD model were strongly supported. (1) The concepts were attained in an invariant sequence at the four successive levels, as predicted. (2) As the concepts were attained at higher levels, they were used increasingly in cognizing supraordinate-subordinate relationships in a hierarchy where the attained concept was an element of the hierarchy; in understanding principles that stated a relationship between the attained concept and one or more other concepts; and in solving problems that required the use of the particular concept. (3) Having the labels of the concept and of its defining attributes facilitated attainment of the concept and mastery of the three uses of the concept. (Author/GDC)