This paper describes three experiments in which computer simulations were employed as tools to modify spontaneous conceptions held by students, thus exploring the possibilities pointed out by the cognitive conflict strategy (Posner et al., 1982). The experiments were designed to try to change spontaneous conceptions found in Mechanic among students in their early years of college, during the study of the laws of Newton. Our approach was based on the use of Prometeus, a new simulation software specially designed for this purpose. Three experiments were performed to verify the suitability of the software and to identify the best teaching strategy to accompany its use. In the rst of them, the program was employed alone, without connection with the teaching sequence adopted by the teacher. Although useful for leading students to question their personal beliefs, this strategy was not enough to bring about significant changes in the ideas they already held. In the second experiment, the program was employed as an instructional resource integrated into the formal teaching, but it was introduced after the classes dealing with the laws of Newton had been offered. Because the results were still not satisfactory, a third experiment was carried out, with some modifications. Its results suggest that the use of Prometeus within the new strategy, in conjunction with the motivation felt by this third group, signi cantly favored the overcoming of misconceptions previously held by these students.
