Jean Piaget theorized that children progress through four distinct stages of cognitive development, characterized by qualitative changes in how they think.
Infants know the world through their senses and motor activities (looking, hearing, touching, mouthing, grasping).
Key Milestone: Object Permanence. The awareness that things continue to exist even when not perceived.
Before ~8 months: "Out of sight, out of mind."
After ~8 months: The child searches for the hidden toy.
Preoperational children struggle with Egocentrism—the inability to take another's viewpoint. They assume you see exactly what they see.
Conservation: Understanding that properties such as mass/volume/number remain the same despite changes in form. Mastered in Concrete Operational.
Formal Operational thinkers use Hypothetico-Deductive Reasoning: systematically testing variables (string length, weight) to determine what makes the pendulum swing faster.