Piaget theorized there are four times when equilibration, inadequate schemes are reorganized or replaced with more advanced and mature schemes, occurs during development. these stages are called:

These stages are called: Piaget's four stages of intellectual (or cognitive) development. They are : a) Sensorimotor. Birth through ages 18-24 months. b) Preoperational. Toddlerhood (18-24 months) through early childhood (age 7) c) Concrete operational. Ages 7 to 12. and d) Formal operational. Adolescence through adulthood.