Mathematics instruction in schools generally employs a uniform approach that does not fully accommodate students’ diverse abilities, needs, and learning characteristics. This condition may lead to low conceptual understanding, particularly in integer topics as a fundamental area in mathematics learning. Although differentiated instruction is considered a potential solution, empirical evidence on its effectiveness in improving junior high school students’ understanding of integers remains limited. Therefore, this study aims to examine the effect of differentiated instruction on students’ understanding of integers in Grade VII at SMP Negeri 1 Ngantru Tulungagung. A quantitative approach was employed using a quasi-experimental design with a Post-Test-Only Control Group Design. The research sample consisted of Class VII-J as the experimental group, which received differentiated instruction integrated with Problem-Based Learning, and Class VII-F as the control group, which received conventional instruction based on Problem-Based Learning. The results showed that the experimental group achieved a higher mean score 81.4 than the control group 64.4. The Independent Samples t-test yielded a significance value of 0.000 < 0.05, indicating that differentiated instruction had a statistically significant effect on students’ understanding of integers. Furthermore, Cohen’s d effect size of 1.3544 indicated a very large effect. These findings provide empirical evidence that differentiated instruction is an effective strategy for improving students’ conceptual understanding of integers. The results also highlight its potential as a more adaptive approach to mathematics instruction that accommodates students’ diverse learning needs.