This study adopts case studies using open-ended questionnaires, pupils' notes, teachers' journals, science fair projects, photos, videos, and other materials in order to explore the use of argumentation in promoting students' elaboration of their science projects. The participants in this study are seven sixth-grade pupils from four different classes, comprising five girls and two boys. The results reveal that the use of argumentation in the elaboration process not only helps the students to examine the validity of science projects but also guides them to reflect on the consistency of the projects' objective, experimental design, results, and conclusion. It was also found that rebuttals are not evident in scientific projects, and though the data claim that warrants are key elements of the elaboration process in a science fair, their meanings are not easily understood by primary-school students. Teachers are required to continuously explain the importance of argumentation. In addition, formulating conclusions based on empirical data is difficult for students. On the other hand, collecting and refining data as evidence to support or disprove a given temporary conclusion are less complicated tasks for the students.