Piaget argued that intelligence develops as children actively construct increasingly powerful ways of organizing experience—not by simply accumulating facts.

Developmental theories ask a question that static ability models cannot answer by themselves: how does a child's way of thinking become an adult form of cognition?

Instead of starting with the correlations among test scores, information-processing approaches ask which mental operations produce intelligent performance.

Godfrey Thomson showed that correlated intelligence-test scores do not logically require one general mental cause. Overlapping samples of many processes can produce a similar pattern.

Open the technical manual of a modern cognitive test and there is a good chance you will encounter three letters: CHC.