The present study focused on investigating the effectiveness of instruction via newly developed teaching materials based on cooperative learning when compared to a traditional approach, on ninth grade students' understanding of metallic bonding. Fifty-seven ninth grade science students from two science classes in the same high school participated in this study. The same teacher taught metallic bonding with cooperative learning to an experimental group (N = 28) and with a traditional teacher centred approach to a control group (N = 29). Students' conceptual understanding of metallic bonding was measured using the Metallic Bonding Concept Test. The results from the Student's t test indicated that the mean score of the students in the experimental group was significantly higher in the experimental group (78.60, SD = 8.62), than in the control group (54.33, SD = 9.11) after treatment. In the light of the results from the concept test and individual interviews, the misconceptions related to metallic bonding were found less in the experimental group than traditional. Five of these misconceptions were firstly identified in this study. The individual interviews which were done with students from experimental group immediately after the instruction showed that students had positive perceptions about their cooperative work experiences.