This study determined the effectiveness of Differentiated Instruction in the reading comprehension level of the Grade-11 senior high school students, school year 2016-2017. Specifically, it aims to determine the reading comprehension level of the control and the experimental groups in the pre test and post-test; identify if there is a significant difference in the reading comprehension level of the control and experimental groups in the pre-test and post-test results; and identify the strengths and weaknesses in using Differentiated Instruction. Quasi-experimental method was employed in conducting the study. The respondents were the 150 Grade-11 students of a public high school grouped as control and experimental using Parallel technique. Data sources include pre-test and post-test scores, gain scores, classroom observation form, survey questionnaire, and researcher's reflective notes. The qualitative data were analysed using template analysis style and the basic approach of comprehending, synthesizing, theorizing and re-contextualizing to identify common themes and integrating thematic pieces. Based on the classroom observations, survey and researcher's reflective notes, strengths and weaknesses of Differentiated Instruction were observed. Despite the observed and encountered challenges, the statistical analysis has revealed a significant difference between pre-test and post-test results.