Jerome Bruner developed concepts around how children learn and develop representations of the world. He proposed that children progress through enactive, iconic, and symbolic representations as they develop. Bruner also developed the idea of a spiral curriculum where the same concepts are revisited at increasing levels of difficulty. His work emphasized the importance of discovery learning where students explore concepts with preparation and guidance from teachers. Bruner identified four major aspects of instruction including predisposition to learn, structure of learning material, sequencing of lessons, and reinforcement. He also studied categorization and proposed rules for how categories are formed based on attributes, combinations of attributes, weight of properties, and acceptance limits.