The problem of defining and measuring intelligence is the problem of defining the constructs that underlie it and of specifying their structure.
The three aspects of intelligence are referred to as processing skills. Rather, development seems to come in intermittent bursts, whose timing can differ from one child to another.
As a child develops, increasingly more accurate models of the world are developed which enable the child to interact with the world better. These four processes are functions of four areas of the brain. The concept of mental age fell into disfavour, however, for two apparent reasons.
On the basis of this definition, intelligence can be reliably measured by standardized tests with obtained scores predicting several broad social outcomes such as educational achievement, job performance, health, and longevity.
In contrast, empirical support for non-g intelligences is lacking or very poor. Suppose that the child is then asked to learn how to solve time-rate-distance problems, having never before dealt with this type of problem.
For example, the concept of mental age was popular during the first half of the 20th century.