Although the identification of the development landmarks is of interest for investigators and for the caretakers of the children, many aspects of the evolutionary change are continuous and are not the remarkable landmarks of the change. [15] changes in the continuous development, the growth like in stature, implies evolution relatively gradual and foreseeable towards the characteristics of the adult. When the evolutionary change is discontinuous, nevertheless, the investigators can identify not only fixed of the development, but the periods related to the age often he is called stages.

A stage is a period of time, often associated with a rank of well-known chronological age, during which a behavior or physical characteristic is qualitatively different from which is in other ages. When a period of age is known like a scene, the term implies not only this qualitative difference, but also a predictable sequence of development events, so that each stage is preceded and followed by other specific periods associated with characteristics of behavior or physical qualities.

Stages of the development can agree or be tie to other specific aspects of the development, as the speech or the movement. Even within a particular area of the development, the transition to a stage does not mean that the previous stage completely is finished. For example, in the discussion of the stages of Erikson of the personality, this theoretician suggests it life is spent in remodeling questions that originally were characteristic of a stage of the childhood. In the same way, the theoretician of the cognitive development, Piaget, describes situations in which the children can solve a kind of problem when using abilities mature reflection, but could not obtain it by less familiar problems, a phenomenon that he called decalage horizontal