SUMMARY
The study aimed to formulate the content of mathematics curriculum at the level of primary school students according to the elaboration theory and measure the effectiveness of this mathematics content to develop academic achievement and critical thinking skills. The study sample comprised (119) students in the fifth grade from Almanahl School in Salalah city of Dhofar Governorate, and was randomly divided into two groups. The first group was the experimental group (60 Students) and the other one was the control group (59 Students). Data were collected via the tests of achievement and critical thinking for the sample in geometric and measurement units. The study was carried out 25 times over 5 weeks. Data were analyzed using means, standard divisions, and T-tests. The study concluded that there was a significant difference at (0.05) between the academic achievement of the experimental group and that of the control group in favor of the experimental group, and there was a significant difference at (0.05) between the critical thinking skills of the experimental group and those of the control group in favor of the experimental group. In light of the results, the study recommended preparing the content of the mathematics curriculum at the basic stage of education following the elaboration theory and improving the mathematics teachers’ performance to develop critical thinking skills for their students.