The study aimed at exploring the effect of using differentiated learning strategy in teaching geometry in the academic achievement and in the mathematical self-concept of the seven grade students in the region of Muscat. The study attempted to answer the main question: "What is effect of differentiated learning strategy in teaching geometry in the academic achievement and in the mathematical self-concept of the seven grade students?". In order to answer the study question, a semi-experimental method was used. The study was applied to sample of (54) students from seven grade. The sample was divided into two group: an experimental group of (27) students learned using differentiated learning strategy, and a control group of (27) students learned in the usual manner. The study found the following results: • There was a statistically significant difference at level of significance (a 0.05) between the average score of the experimental group and the average score of the control group in the post-test of the academic achievement in favor of the mean scores of the experimental group. There is a statistically significant difference at level of significance (ac0.05) between the average score of the experimental group and the average score of the control group in the post-application of the measure of the self-concept of sports in favor of the average scores of the experimental group. Considering these results, recommended the use of differentiated learning strategy in the teaching of different math subjects, because the study showed appositive effect in raising the achievement level in students.