About the Author: (from TheAmerican Mathematical Monthly, vol.  87, (1980)) Alan H. Schoenfeld received his Ph.D. from Stanford in 1973, working under Karel deLeeuw in topology and measure theory.  After two years at Davis he joined the SESAME group at U.C. Berkeley, where he began his current “research and development in ‘human AI’ where the research goal is to create detailed models of human problem-solving, the development goal to use the models to teach students to solve problems the way experts do.”  He would like to hear from colleagues who are either studying or trying to teach problem solving.  The author dedicates this paper to the memory of Karel deLeeuw, in appreciation of his spirit of inquiry and his devotion to his students.