This study aimed to identify the effect of using a constructivist learning model in teaching the unit of geometry and spatial sense on mathematics achievement and creative thinking of seventh basic stage students. To achieve this, the researcher prepared a teacher's guide, to teach mathematics using a constructivist learning model. The researcher used an achievement test in mathematics, and Torrance's creativity thinking test. The sample of the study was selected. This sample consisted of (123) students of grade seven. The sample was divided into two groups, the experimental group which was taught using the constructivist learning model and the control group which was taught by using the usual method. After finishing teaching, an achievement test and a creativity thinking test were applied on students of both groups. The results of the study showed the superiority of students of the experimental group in the achievement and the creativity thinking test. The researcher recommends to encourage teachers to use a constructivist learning model in teaching and she emphasizes the importance of developing the creative thinking in mathematics.