Cognitive Development-Piaget's stages of Development

Human development to adulthood is longer than that of other mammals to allow time for growth of a large brain and acquisition of a large amount of knowledge.
Piaget’s Stages of Development
Developmental psychologists have tried to understand the intellectual changes that take place as we grow from infancy through adulthood. Many have been particularly influenced by the Swiss psychologist Jean Piaget, who studied and theorized about child development for more than half a century. Much of the recent information-processing work in cognitive development has been concerned with correcting and restructuring Piaget’s theory of cog- nitive development. Despite these revisions, his research has organized a large set of qualitative observations about cognitive development spanning the period from birth to adulthood. Therefore, it is worthwhile to review these observations to get a picture of the general nature of cognitive development during childhood.
According to Piaget, a child enters the world lacking virtually all the basic cognitive competencies of an adult but gradually develops these competencies by passing through a series of stages of development. Piaget distinguishes four major stages. The sensory-motor stage is in the first 2 years of life. In this stage, children develop schemes for thinking about the physical world—for instance, they develop the notion of an object as a permanent thing in the world.
The second stage is the preoperational stage, which is characterized as spanning the period from 2 to 7 years of age. Unlike the younger child, a child in this pe- riod can engage in internal thought about the world, but these mental processes are intuitive and lack systematicity. For instance, a 4-year-old who was asked to describe his painting of a farm and some animals said, “First, over here is a house where the animals live. I live in a house. So do my mommy and daddy. This is a horse. I saw horses on TV. Do you have a TV?”
The third stage is the concrete-operational stage, which spans the period from age 7 to age 11. In this period, children develop a set of mental opera- tions that allow them to treat the physical world in a systematic way. However, children still have major limitations on their capacity to reason formally about the world. The capacity for formal reasoning emerges in Piaget’s fourth period, the formal-operational stage, spanning the years from 11 to adulthood. Upon entering this period, although there is still much to learn, a child has become an adult cognitively and is capable of scientific reasoning—which Piaget took as the paradigm case of mature intellectual functioning.
Piaget’s concept of a stage has always been a sore point in developmental psychology. Obviously, a child does not suddenly change on an 11th birthday from the stage of concrete operations to the stage of formal operations. There are large differences among children and cultures, and the ages given are just approximations. However, careful analysis of the development within a single child also fails to find abrupt changes at any age. One response to this gradu- alness has been to break down the stages into smaller substages. Another re- sponse has been to interpret stages as simply ways of characterizing what is inherently a gradual and continuous process. Siegler (1996) argued that, on careful analysis, all cognitive development is continuous and gradual. He char- acterized the belief that children progress through discrete stages as “the myth of the immaculate transition.”
Just as important as Piaget’s stage analysis is his analysis of children’s performance on specific tasks within these stages. These task analyses provide the empirical substance to back up his broad and abstract characterization
of the stages. Probably his most well-known task analysis is his research on conservation, considered next.
■ Piaget proposed that children progress through four stages of in- creasing intellectual sophistication: sensory-motor, preoperational, concrete-operational, and formal-operational.