Piaget

Meaning: Piaget described children as active learners who build schemas, mental frameworks for organizing knowledge. Assimilation fits new information into an existing schema; accommodation changes the schema when the information does not fit. The stages, with approximate ages, are sensorimotor (birth to about 2: learning through senses and actions, object permanence), preoperational (about 2 to 7: symbols and language, egocentrism, centration, no conservation), concrete operational (about 7 to 11: conservation, logical thought about concrete objects), and formal operational (about 11 onward: abstract and hypothetical reasoning).

On the MCAT: A vignette describes a child's behavior and asks for the stage. A child who searches for a hidden toy shows object permanence. A child who says a tall narrow glass holds more water than a short wide one, though the water was only poured from one to the other, has not yet achieved conservation (preoperational). A child who reasons about hypothetical "what if" problems is formal operational. Questions also ask you to label an example as assimilation or accommodation.

Common confusion: Students swap assimilation and accommodation. Assimilation keeps the schema and fits the input into it; accommodation modifies the schema. Also, the ages are approximate, though the order of stages is fixed in the theory. Vygotsky, by contrast, stressed social interaction in development.