Biological maturation also plays an important role: As the brain and nervous systems mature, children become capable of increasingly complex cognitive schemes that help them to construct better understandings of what they have experienced (Piaget, 1970). Eventually, curious, active children, who are always forming new schemes and reorganiz�ing their knowledge, progress far enough to think about old issues in entirely new ways; that is, they pass from one stage of cognitive development to the next higher stage.Four Stages of Cognitive DevelopmentPiaget proposed four major stages of cognitive development: the sensorimotor stage (birth to age 2), the preoperational stage (ages 2 to 7), the concrete-operational stage (ages 7 to 11–12), and the formal-operational stage (ages 11–12 and beyond). These stages form what Piaget called an invariant developmental sequence—that is, all children progress through the stages in exactly the order in which they are listed. They cannot skip stages because each successive stage builds on the previous stage and represents a more com�plex way of thinking.Table 2.3 summarizes the key features of Piaget’s four cognitive stages. Each of these periods of intellectual growth will be discussed in much greater detail when we return to the topic of cognitive development in Chapter 7.Contribu