This study determined the effect of code-switching on errors in integer operations among Grade 7 learners at Crisanto M. Ciriaco Integrated School, Concepcion, Iloilo, during the School Year 2025–2026. A quasi-experimental non-equivalent control group pretest–posttest design was employed, involving sixty (60) learners, with thirty (30) assigned to the experimental group and thirty (30) to the control group. The experimental group received instruction through intentional code-switching (English–Hiligaynon), while the control group was taught using English-only instruction. A validated 40-item researcher-made test was used to gather data. Descriptive and inferential statistics were applied at a 0.05 level of significance. Results revealed that both groups had comparable pretest performance at the Low Proficiency level. After the intervention, the experimental group improved to Nearly Proficient, while the control group remained at Low Proficiency. A statistically significant difference in posttest performance was found in favor of the experimental group. Moreover, only the experimental group showed significant improvement from pretest to posttest. In terms of error reduction, the experimental group demonstrated a substantially greater decrease in errors compared to the control group. The findings indicate that teacher-led code-switching is an effective instructional strategy for improving mathematics performance and reducing errors in integer operations. The study recommends the integration of code-switching in mathematics instruction to enhance learners’ comprehension and learning outcomes.