Abstract
The recently reviewed primary school mathematics curriculum in Malaysia expects students to be provided with opportunities to develop their mathematical thinking. At the moment, not much is known about the extent of the development of primary school students’ mathematical thinking. The traditional paper-and-pencil achievement tests normally given to students are not sufficient in assessing the true picture of the students’ mathematical thinking. To assess students’ mathematical thinking, teachers need to use assessment techniques that will collect evidence about the students’ mathematical thinking process. This paper plans to show several examples how teachers might assess students’ mathematical thinking through open ended tasks. The tasks will involve students making decisions and justifying the decisions they had made. To analyze and interpret students’ response, this paper will show how an assessment rubric can be used.