Piaget described cognitive development as occurring in :

The correct answer is Four qualitatively different stages.

Educational Explanation:
Jean Piaget, a renowned Swiss psychologist, proposed a comprehensive theory of cognitive development. According to Piaget, children progress through cognitive development in a series of distinct stages. Rather than simply acquiring more knowledge continuously, children at different ages think in fundamentally distinct ways.

Piaget identified four qualitatively different stages of cognitive development:
1. Sensorimotor Stage (Birth to 2 years): Infants explore the world through sensory experiences and motor activities, developing concepts such as object permanence.
2. Preoperational Stage (2 to 7 years): Symbolic thought emerges, and language skills develop rapidly, though thinking remains largely egocentric and non-logical.
3. Concrete Operational Stage (7 to 11 years): Children begin to think logically about concrete events and master concepts of conservation and categorization.
4. Formal Operational Stage (12 years and above): Individuals develop abstract, hypothetical, and systematic reasoning capabilities.

These stages are considered "qualitatively different" because each represents a new level of cognitive organization and a distinct way of understanding reality.