Proster Theory is a theory of learning which has been proposed by Leslie A. Hart (1975). The theory is based on the functions of the brain. Learning is seen as the formation of programs, which are simply sequences of instructions by which the brain directs the muscles, sense organs, or other portions of the neurological system. Programs which are related are organized into structures called prosters. The theory also identifies two types of thinking: SSM (symbol selection and manipulation) thinking which is conscious and step-by-step, and PAC (perception, analysis, choice) thinking which is intuitive or "natural." There may be some relationship between the PAC/SSM distinction and the distinction of concrete operational thought from formal operational thought in Piagetian theory. This relationship and its educational implications are discussed. (BW)