This is a report on the investigation of a microcomputer-based system for the diagnosis and remediation of three Aristotelian alternative conceptions of force and motion held by eighth-grade physical science students. Diagnosis and posttesting were done with computer-displayed, graphics-based, multiple-choice questions. The two remediation simulations were designed to present scientific idealizations and to be perceived by the student as anomalous to the three alternative conceptions. Structured interviews were employed at several points during the study to obtain indications of the conceptions of force and motion of students with different achievement rankings, as well as to determine the students' reactions to the computer pretest questions or the simulations. A student's possession of alternative conceptions was unrelated to whether the student was a strong or weak learner of science. Students who were currently studying dynamics in their classes exhibited a very different pattern of nonscientific answers on the computer diagnostic test than did students who had completed that topic. The completed students who were selected for possession of alternative conceptions were facilitated by the computer simulations in altering their naive conceptions to a significant degree.