Intellectual development is a vast topic – far too large even to begin to summarize in a single, relatively brief chapter. Therefore, this review is, of necessity, extremely selective. It includes two sections. The first briefly describes six theories of intellectual development, three longstanding ones and three more recent ones. The second focuses on a core area of intellectual development in which progress has been especially notable over the two decades since the previous edition of this handbook: the development of problem solving and learning.

THEORETICAL APPROACHES

Traditional Theories

psychometric approaches. Psychometric theories are aimed at explaining individual and developmental differences in performance on standardized tests of intellectual performance – especially IQ tests. Underlying such theories is the assumption that intelligence can be assessed in terms of latent sources of individual differences or “factors.” Psychometric theories can be divided by the number of factors that they emphasize: one, a few, or many. Consider a prominent example of each. Spearman (1927) emphasized that underlying all intellectual performance is a single common general factor (g). Thurstone (1938) proposed that intelligence involves seven primary mental abilities: verbal comprehension, verbal fluency, number, spatial visualization, memory, reasoning, and perceptual speed. Guilford (1967) hypothesized the existence of 180 ability factors based on the possible combinations of three dimensions that were present in all tasks: content, operation, and product. The one-few-many trichotomy also applies to nonpsychometric theories of intellectual development.