Jerome Bruner developed a theory of cognitive development that occurs in three stages - enactive, iconic, and symbolic. In the enactive stage, knowledge is represented through motor actions and skills. In the iconic stage, knowledge is represented through mental images and diagrams. In the symbolic stage, knowledge is represented through language, words, and other abstract symbol systems. Bruner believed that scaffolding from teachers and discovery learning were important for cognitive growth as students develop more complex thinking abilities through these sequential stages.