Piaget's organismic-developmental theory of intelligence was investigated in this study to determine the effectiveness of training middle class 3 and 4 year olds on two logico-mathematical structures: classification and seriation. Twenty-four children were divided into two main age groups (mean ages: 3 years 8 months; 4 years 5 months). Within each age category, children were randomly assigned to groups of four for seriation training, classification training, and a control group. To assess IQ and verbal ability, the Peabody Picture Vocabulary Test was utilized as a pretest-posttest measure; Piagetian tasks as a posttest only. Tasks included a seriation series of six problems and a classification series of seven problems. Three conservation tasks (quantity, number and area) were administered as far-transfer tests. Covariance analysis of the seriation task battery indicated there were significant treatment main effects and an age-treatment interaction with the high age seriation group indicating superior performance. Classification in both age groups was not found to be effective. Learning was not found to generalize to the far-transfer tasks. The age-related findings from this study were interpreted as supporting the stage-dependent aspects of Piaget's theory. (Author/AJ)