The current study aimed to find the effectiveness of Differentiated Instruction in Algebraic Thinking and Motivation in Mathematics among seventh grade female students in Oman. A quasi-experimental curriculum was used. The randomly selected sample (n=62) were divided into two groups. Experimental group (n= 31) was taught the unit of “the Graphs” through Differentiated Instruction. Controlled group (n= 31) was taught the same unit using the usual teaching methods. To verify this, the researcher designed a teacher's guide to teach the unit of “the Graphs” by using Differentiated Instruction. Both groups sat for Algebraic Thinking test designed by the researcher consisted of 13 questions and a scale of Motivation in Mathematics consisting of 20 phrases, which were checked and found reliable and stable. The study found that there is a statically significant difference at the level of (α= .05)) between the arithmetic mean of experimental group students who studied by Differentiated Instruction, and the arithmetic mean of control group who studied using the usual teaching method in Algebraic Thinking and Motivation in Mathematics in favor of the experimental group. Considering these results, the researcher recommended to start using Differentiated Instruction in teaching Mathematics for the lower grades students. Further studies were recommended to compare Differentiated Instruction with new teaching methods, which effects learning quality, student achievements and enhances thinking skills.