Cognitive development refers to the development of the ability to think and reason.

Children (typically 6 to 12 years old) develop the ability to think in concrete ways (concrete operations), such as how to combine (addition), separate (subtract or divide), order (alphabetize and sort), and transform (5 pennies = 1 nickel) objects and actions. These processes are called concrete because they are performed in the presence of the objects and events being thought about.

Adolescence marks the beginning development of more complex thinking processes (also called formal logical operations) including abstract thinking (thinking about possibilities), the ability to reason from known principles (form own new ideas or questions), the ability to consider many points of view according to varying criteria (compare or debate ideas or opinions), and the ability to consider the process of thinking.