IT is late afternoon, but the four-year-old insists: “It can’t be. I haven’t had my nap.” Such is the mind of the child, by most indications illogical and full of nonsense. Not so, says Jean Piaget, a ...

Jean Piaget’s theory of cognitive development has been a central framework for understanding how children grow and learn. His model describes development through four sequential stages: sensorimotor, ...