According to Piaget, knowledge does not exist somewhere outside of the mind.  As people interact with their environment, they interpret what they experience.  In doing so, they actively “construct” knowledge by forming categories of associations.  Rather than impart knowledge to students through lectures and reading, the teacher’s role is to help students build schemas by having them actively experiment and explore the world.  When students encounter new experiences, they feel cognitive disequilibrium, which is uncomfortable, so they attempt to restore equilibrium by either “assimilating” information about the new experience into their existing schemas, or by “accommodating” the information through changing their mental frameworks (altering their schematic structures).  The greater the variety of experiences the student has, the more information he or she will need to incorporate through assimilation and accommodation, leading to more accurate knowledge structures. 

Another key idea presented by Piaget is that people go through stages of development.  They have different cognitive abilities at each stage.  A person cannot learn in a way for which she or he is not cognitively able, so teachers should be sensitive to what students are able to do at each age when presenting new concepts.