This study sought to explore the effect of Differentiated Instruction, in light of learners' cognitive profiles, on female English as a Foreign Language (EFL) foundation year students' learning of grammar at King Abdul-Aziz University in 2017-2018. Following a pretest-intervention-posttest experimental design, the first part of the study aimed at exploring the phenomenon from a positivist point of view. The second, on the other hand, attempted to grasp the way learners perceive Differentiated Instruction through short one-to-one interviews of the participants. The quantitative results revealed that although the application of Differentiated Instruction made a significant difference between the pretest and posttest results of students in the experimental group, the difference in performance between these students and their counterparts in the control group was not statistically significant. The qualitative results, on the other hand, revealed that learners perceive the application of Differentiated Instruction in a positive manner. Three themes were found to be recurrent in their responses: the increased motivation, appropriateness of access, and autonomy. Based on these findings, a few implications and recommendations were drawn.