Characteristics of each stage:
1. The sensorimotor stage (0 - 2 years)
Appearance of self-preservation instincts.
Assimilation of new information.
Development of sensori-motor reactions, reflexes and first schemata.
Perception of object permanence.
Problem solving by sudden mental operations.
2. Preoperational stage (2 - 7 years)
Egocentrism (children are unable to understand other than their own perceptions).
Perception of object conservation (objects change place without alteration of their physical properties of matter).
3. Concrete operational stage (7 - 11 years)
Problem solving involving concrete thinking (present objects).
Full development of perception of object permanence.
Development of inductive logic.
4. Formal operational stage (adolescence - adulthood)
Problem solving involving concrete and abstract thinking.
Development of deductive logic.
Piaget, J., Inhelder, B. (1969). La Psicología del Niño. Morata. París.