Organization and adaptation are what Piaget called invariant functions. This means that these thought processes function the same way for infants, children, adolescents, and adults. Schemes, however, are not invariant. They undergo systematic change at particular points in time. As a result, there are real differences between the ways younger children and older children think and between the ways children the adults think. The schemes of infants and toddlers, for example, are sensory and motor in nature. They are often referred to as habits or reflexes. In early childhood, schemes gradually become more mental in nature; during this period, they are called concepts or categories. Finally, by late adolescence or early adulthood, schemes are complex and result in what we call strategic or planful behavior.