AbstractThe aim of this study is to investigate the effects of argumentation model on students’ achievement on the unit of “States of Matter and Heat”, and also to determine how to change students’ argumentation skills during the instruction through argumentation model. Semi-experimental design was used in this study. The sample was comprised of totally 40 eight grade students from two different classes in a primary school. An achievement test and semi-structured interviews were used to collect data. The achievement test was implemented to both experimental and control groups as pre- and post-tests. Semi-structured interviews were conducted with students to determine students’ views about the lessons in which argumentation model was used. Also, all discussions in the science lessons were audio recorded to determine how to change students’ argumentation skills during the instruction of the unit. Results showed that argumentation model had positive effects on students’ achievement and conceptual understanding on the unit, and there was a significant difference between experimental and control groups in favor of the experimental group. Moreover, the analyses of the data obtained from the interviews and audio recordings clearly indicated that experimental group students’ argumentation skills were improved gradually during the instruction.