This document discusses cognitive development theory and Piaget's stages of cognitive development. It provides an overview of Piaget's four stages of cognitive development from infancy to adulthood, including the age bands and how children understand the world at each stage. The stages are sensorimotor (birth to 2 years), preoperational (2 to 7 years), concrete operational (7 to 12 years), and formal operational (above 12 years). The document also acknowledges the NPTEL core team for the academic writing course and provides references related to cognitive development and academic writing.