Piaget's stages

Meaning: Piaget's theory describes cognitive development as four stages in a set order, each a qualitatively different way of thinking. Children build and revise schemas through assimilation (fitting new information into an existing schema) and accommodation (changing the schema to fit the information).

Sensorimotor (birth to about 2): learning through senses and actions; object permanence appears. Preoperational (about 2 to 7): symbolic thought, pretend play, egocentrism, centration, no conservation. Concrete operational (about 7 to 11): logical thinking about concrete objects, conservation, reversibility. Formal operational (about 11 onward): abstract, hypothetical, deductive reasoning.

On the MCAT: A vignette describes a child's behavior and asks for the stage. A toddler hunting for a hidden toy suggests sensorimotor. A child who says a tall thin glass holds more water than a short wide one suggests preoperational. A child who says the amounts are equal because the water could be poured back suggests concrete operational. A teen testing hypotheses systematically suggests formal operational.

Common confusion: The ages are approximate; the fixed claim is the order. Egocentrism means difficulty taking another person's viewpoint, not selfishness. Object permanence is a sensorimotor milestone, while conservation is achieved later, in the concrete operational stage.