Abstract
The use of valid argument does not come natu-rally. It is acquired only through practice. This study was accomplished to provide students intended opportunities of engaging activities for launching argumentation in primary classrooms. The focus of the paper is how argumentation was evolved when students engaged in the conjecturing incorporated into regular mathematics instruction over two consecutive years. Working with a group of 6 teachers was to develop conjecturing tasks and pedagogical strategies to support them in teaching, and then to enhance the quality of students’ argumentation when 24 students were in grades 3 and 4. The collected data mainly consisted of conjecturing tasks, audio – and video – taped recordings of classroom observations, and stu-dents’ worksheets. Results indicate that the evolution of argumentation was identified in two aspects: the characteristics and the quality of the argumentation.