Effects of Mother Tongue-Based Instruction in Geometry on the Performance of Grade 7 Learners

This quasi-experimental study improved the mathematical learning performance in geometry of Grade 7 learners at Aflek National High School – Edwards National High School Annex, Aflek, Tboli, South Cotabato, during the third quarter of School Year 2025–2026 through the implementation of Mother Tongue–Based Instruction. Before the intervention, both the control group, which received Traditional Instruction using English, and the experimental group, which received Mother Tongue–Based Instruction using Blaan, exhibited a poor level of mathematical competency. After the implementation of the intervention, the posttest results revealed that while both groups showed improvement, the experimental group demonstrated a significantly greater increase in performance. The overall competency level of the experimental group improved from Poor to Good. Statistical analysis further showed that the mean score of the experimental group was significantly higher than that of the control group, indicating the effectiveness of Mother Tongue–Based Instruction. Hence, the Department of Education and school administrators are encouraged to support the development and utilization of localized instructional materials and to provide continuous teacher training on effective Mother Tongue–Based teaching strategies to improve learning outcomes in mathematics.