This paper, presented at the 1979 meeting of the American Educational Research Association (AERA), investigates student errors in high school mathematics. A conceptual framework of hypothetical information-handling processes such as procedures, frames, retrieval from memory, visually-moderated sequences (VMS sequences), the integrated sequence, and meta-language are suggested to interpret the observations of students learning arithmetic, algebra, geometry, and calculus. Some of the errors discussed are: (1) random errors vs. regular errors; (2) VMS sequence errors; (3) frame errors; (4) language-related errors; (5) abstract verbal statements; (6) epistemological errors; and (7) the persistence of incorrect rules of procedures. (HM)