Piaget's stages of cognitive development
Piaget's stages of cognitive development
1- Sensorimotor - 0-2 yrs

2- Preoperational - 2-7yrs

3- Concrete operational - 7-11yrs

4- Formal operational - 11-adult, only about 50% of adults reach this stage

Formalized by the Swiss psychologist Jean Piaget
At wikipedia, Details - more details
Good discussion of Piagetan development
Cognitive development theories