The document summarizes Piaget's theory of cognitive development and its implications for mathematics instruction. It describes the four stages of cognitive development according to Piaget - sensorimotor, preoperational, concrete operational, and formal operational. For each stage, it provides examples of characteristics and abilities, as well as suggestions for developmentally appropriate mathematics activities and instruction. The summary concludes that understanding Piaget's stages helps teachers plan activities matched to students' cognitive levels to support mathematical development.