The document summarizes Jean Piaget's four stages of cognitive development:
1) Sensorimotor stage (birth to 2 years) where intelligence develops through physical interactions and experiences without symbols.
2) Pre-operational stage (2 to 7 years) where symbols and language develop but thinking is non-logical.
3) Concrete operational stage (7 to 11 years) where logical and systematic thinking about concrete objects develops.
4) Formal operational stage (11 years to adulthood) where logical thinking with abstract concepts develops but some egocentric thought returns.