The question examined in this paper is: what is known exactly about variables that affect long-term retention of knowledge learned in school? U. Neisser (1982) asserts that "it is difficult to find even a single study, ancient or modern, of what is retained from academic instruction." Further, popular belief holds that much of the knowledge learned in classrooms is forgotten shortly thereafter. Contrary to these assertions, several studies published in content area journals have addressed this question and found substantial long-term retention. These and other studies are examined to determine how much of the knowledge and principles learned in college classrooms is remembered. Several variables that affect the ability to remember are discussed, including the level of original learning, overlearning, the method of instruction, characteristics of the retention interval, the type of information taught and tested, and individual differences in aptitude and motivation. In general, methods that promote higher levels of original learning produce higher levels of retention. A list of 64 references is included. (Author/SLD)