This present study examined how interventions based on students’ prior knowledge facilitates their conceptual understanding. Individual experiments were conducted on seventh graders (N=39 in Experiment 1; N=38 in Experiment 2), and they solved some problems about oxidation reaction in 3 sessions: pre-test, intervention (2 conditions: experimental or control), and post-test. In Experiment 1, students’ in experimental condition reasoned condition of a thing through time using pictures. On the other hand, students’ in control condition were showed a thing in pictures. The results indicated that (a) three levels were identified, (b) the experimental condition facilitated the understanding, and (c) understanding deepening in the intervention were related to that in the post-test. The purpose of Experiment 2 was to investigate the intervention of Experiment 1, and a real thing was used in place of pictures. The results showed that (a) the experimental condition facilitated the understanding, (b) understanding deepening in the intervention was related to that in the post-test, and (c) Experiment 2 had the more effect on the understanding than Experiment 1.
