In this study, we investigated the relationships among cognitive conflict and situational interest induced by a discrepant event, attention and effort allocated to learning, and conceptual change in learning the concept of density. Subjects were 183 seventh graders from six middle schools in Seoul, Korea. A preconception test, a test of responses to a discrepant event, and a questionnaire of situational interest were administered as pretests. Computer-assisted instruction was then provided to the students as a conceptual change intervention. Questionnaires regarding attention and effort, and a conception test were administered as posttests. The conception test was administered once more as a retention test four weeks later. The results of path analysis indicated that both cognitive conflict and situational interest induced by a discrepant event respectively had an indirect effect on students‘ conceptual understanding, which were mediated by attention and effort allocated to concept learning. Situational interest, however, was found to exert a stronger influence on conceptual change than cognitive conflict. It was also found that attention, either directly or indirectly through effort, influenced students‘ conceptual understanding.