How did Piaget develop most of his theories about children's development?

Piaget's theories about children's cognitive development were primarily developed through careful observation of his own children as they grew. He was particularly interested in how they interacted with their environment and how their thinking evolved over time. This hands-on approach allowed him to see firsthand the stages of development and the types of reasoning children employed at various ages. By documenting their behaviors, mistakes, and learning processes, he was able to formulate his theory of cognitive development, which includes concepts like schemas, assimilation, and accommodation.

This direct observation was crucial because it provided Piaget with real-life examples of the cognitive processes he aimed to describe. In contrast to methods like conducting controlled experiments or extensive surveys, his observations offered a qualitative, in-depth understanding of how children think and learn, leading to his influential theories in developmental psychology.