Every classroom has a mixed section of learners based on their level of intelligence and performance criteria. This mixed section includes Slow learners who cannot keep up scholastically with their age mates and struggle to cope with the traditional academic demands of the regular classroom. They have the ability to acquire all necessary academic skills, but at a rate and depth below that of the average student. So the challenge for the teachers is to understand the areas of interests of slow learners and adopt different teaching learning strategies which can help in improving their cognitive skills. In the present study, the researcher investigates the effect of differentiated instruction on cognitive skills of slow learners. The sample was drawn from various schools of Chandigarh. It consisted of 40 slow learners of grade 4 from both the genders. Initially random sampling technique was used for the selection of government schools of Chandigarh. After that, slow learners were identified purposively by administering various tools. The present investigation utilized experimental method with pre-test, post-test control group design with two experimental groups. Self prepared cognitive skill test and self prepared instructional material or teaching modules were used. Mean, standard deviation and anova t-ratio were used to arrive at the following conclusion that the effect of differentiated instruction is statistically significant on the cognitive skills of fourth grade slow learners.