The aims of the study were to explore the effects of teaching heuristics in a calculus course and to generate hypotheses about related changes in heuristic usage and problem solving performance. Thirty college students in two classes participated and a Solomon four-group research design was used. Students from one group in each class were interviewed individually and asked to solve word problems aloud, then an instructional program was given in which one class received heuristic-oriented instruction while the other class did not. A second diagnostic observation was held. Results indicate that heuristic subjects exhibited superior performance on approach, plan, and result; showed less difficulty in terms of hesitation and reading the problem; and exhibited slightly decreased solution time and markedly increased time in checking the results than the control group. (Author/DT)