Jean Piaget (1896-1980) was a Swiss philosopher and psychologist. His lifelong passion was to understand how humans create knowledge. Piaget's efforts founded the discipline of genetic epistemology (biological foundations for knowledge), and established a framework that continues to affect the way teachers are trained and students are taught.
Piaget spent years observing and interviewing young children in an effort to further his theories about the construction of knowledge. He thought that by observing the ways that children create meaning, he could learn more in general about the development of knowledge.
From these observations, Piaget came to his theory that the development of knowledge is based on cognitive structure. Cognitive structures are understood to be the ways that young people make sense of the world, given their lack of adult sensibilities. Each cognitive structure is well defined by a series of traits, and corresponds loosely to specific ages: sensorimotor, 0-2 years; preoperation, 3-7 years; concrete operation, 8-11 years; formal operation, 12-15 years.
Based on his studies, Piaget felt strongly that students should not be seen as empty vessels to be filled by expert teachers, but rather active participants in the building of their own knowledge. The explanations they offer for natural phenomena, for example, may be incorrect according to our adult sensibilities and research, but the fact that children do offer explanations for these things shows that they are actively working to understand the world around them.
It is no wonder that he so valued the intelligence of young people. Jean Piaget composed his first academic paper at the age of 10, when he observed curiosities about an albino sparrow that could not be explained without the aid of a university library. In an effort to gain the respect of the librarian, and thus access to the library, he wrote the first of his several hundred articles. Although not Piaget's primary academic focus, biology and natural history were things he studied and wrote about with passion throughout his life.