Piaget's theory of cognitive development describes 4 stages of development: 1) Sensorimotor stage (birth to age 2) where intelligence develops through experiences and motor skills without use of symbols. 2) Preoperational stage (ages 2 to 7) where symbolic thought and language develop but thinking remains egocentric. 3) Concrete operational stage (ages 7 to 11) where logical and methodical thought allows for problem solving without real-world experiences. 4) Formal operational stage (age 11 onward) where abstract thinking allows for reasoning about hypothetical concepts and formation of hypotheses.