The period of is most clearly defined by Jean Piaget and his definition, the formal-Operations stage. One of Piaget's four stages of Cognitive Development, it involves characteristics of advanced reasoning, creativity, grasping of external concepts and thinking more extensively. Criticisms of this theory, are it's lack of flexibility in a child's ability to attain Formal-Operations stage, and that children can attain these characteristics earlier or later than Piaget's pre-determined age bracket. It is the expressing of these new found abilit ....