The purpose of this study was to investigate the effects of the Common Knowledge Construction Model (CKCM) lesson sequence, an intervention based both in conceptual change theory and in Phenomenography, a subset of conceptual change theory. A mixed approach was used to investigate whether this model had a significant effect on 7th grade students' science achievement and conceptual change. The Excretion Unit Achievement Test (EUAT) indicated that students (N = 33) in the experimental group achieved significantly higher scores (p less than 0.001) than students in the control group (N = 35) taught by traditional teaching methods. Qualitative analysis of students' pre- and post-teaching conceptions of excretion revealed (1) the addition and deletion of ideas from pre- to post-teaching; (2) the change in the number of students within categories of ideas; (3) the replacement of everyday language with scientific labels; and (4) the difference in the complexity of students' responses from pre- to post-teaching. These findings contribute to the literature on teaching that incorporates students' conceptions and conceptual change. (Contains 5 figures and 4 tables.)