Development of intelligence

There have been a number of approaches to the study of the development of intelligence. Psychometric theorists, for instance, have sought to understand how intelligence develops in terms of changes in the factors of intelligence over time and changes in the amounts of the various abilities that children have. For example, the concept of mental age was popular during the first half of the 20th century. A given mental age was held to represent an average child's level of mental functioning for a given chronological age. Thus, an average 12-year-old would have a mental age of 12, but an above-average 10-year-old or a below-average 14-year-old might also have a mental age of 12 years. The concept of mental age fell into disfavour, however, and has come to be used only rarely. Two main reasons appear to have caused this change. First, the concept does not seem to work after about the age of 16. The mental test performance of, say, a 25-year-old is generally no better than that of a 24- or 23-year-old. Furthermore, in later adulthood some test scores seem to start declining. Second, many psychologists believe that intellectual development does not exhibit the kind of smooth continuity that the concept of mental age appears to imply. Rather, development seems to come in intermittent bursts, whose timing can differ from one child to another.

Jean Piaget's work

The landmark work in intellectual development has not come out of psychometry but rather out of a tradition forged by the Swiss psychologist Jean Piaget. Over the course of a long career, Piaget formulated what became one of the monumental theories in the history of psychology. Two of its main aspects concern the mechanisms by which intellectual development takes place and the periods through which children develop. As modeled by Piaget, the child explores the world and observes regularities and makes generalizations, much as a scientist does. The first part of Piaget's theory recognizes two fundamental cognitive processes that work in somewhat reciprocal fashion. The first is what Piaget called assimilation, a process that involves incorporating new information into an already existing cognitive structure. Suppose, for example, that a child knows how to solve problems that require a percentage of a given number to be calculated. The child then learns how to solve problems that ask what percentage of a number another number is. The child already has a cognitive structure, or what Piaget called a "schema," for percentage problems and can incorporate the new knowledge into the existing structure. But suppose the child is to learn next how to solve time-rate-distance problems, never before having dealt with this type of problem. In this case, the child may need to call upon the second process, accommodation, to form a new cognitive structure that can incorporate the new information. Cognitive development, according to Piaget, represents a dynamic equilibrium between the two processes of assimilation and accommodation.

The second part of Piaget's theory postulates that there are four major periods in intellectual development. The first, the sensorimotor period, extends from birth through roughly two years of age. During this period, a child learns how to modify reflexes to make them more adaptive, to coordinate actions, to retrieve hidden objects, and, eventually, to begin representing information mentally. During the second, preoperational, period from about two to seven years of age, a child experiences the growth of language and mental imagery and learns to focus on single perceptual dimensions, such as colour and size. The third, concrete-operational, period from about seven to 12 years of age is the time during which a child develops an important set of skills referred to as conservation skills. For example, suppose that water is poured from a wide, short beaker into a tall and narrow one. A preoperational child, asked which beaker has more water, will say that the second beaker does (the tall, thin one); a concrete-operational child, however, will recognize that the amount of water in the beakers must be the same. Finally, children emerge into the fourth, formal-operational, period, which begins about age 12 and continues throughout life. The formal-operational child develops thinking skills in all logical combinations and learns to think with abstract concepts. For example, a concrete-operational child asked to determine all possible orderings, or permutations, of four digits, such as 3-7-5-8, will have great difficulty doing so. The formal-operational child, however, will adopt a strategy of systematically varying alternations of digits, starting perhaps with the last digit and working toward the first. This systematic way of thinking is not possible for the normal concrete-operational child.

Piaget's theory had a major impact on the views of intellectual development, but the theory no longer has the widespread acceptance it once had, particularly from the 1950s through the 1970s. One reason for this is that the theory deals primarily with scientific and logical modes of thought and much less with aesthetic, intuitive, and other modes of thought. Another reason is that Piaget tended to overestimate the ages at which children could first perform certain cognitive tasks. Despite its diminished influence, however, Piaget's theory continues to serve as a basis for other theories.

Contents of this article:

Introduction
Cognitive-contextual theories and biologic theories
Hemispheric studies
Development of intelligence
Post-Piaget theories and the environmental viewpoint
Measuring intelligence
The distribution of IQ scores and the malleability of intelligence