Piaget's theory proposes four stages of cognitive development: the sensorimotor stage from birth to age 2, the preoperational stage from ages 2 to 7, the concrete operational stage from ages 7 to 11, and the formal operational stage from adolescence to adulthood. Teaching implications of Piaget's theory include focusing on the thinking process rather than just answers, encouraging active student involvement in learning, avoiding accelerating development, accepting individual differences in progress, and adapting instruction to match the developmental level of the learner.