This study examined the impact of contextualized and localized instructional materials and worktexts on the academic achievement of Grade IV learners in Mathematics. A quasi-experimental and quantitative correlational research design was employed to investigate the effects of these materials on the numeracy levels and computational skills of 110 Grade IV learners. Using a purposive sampling technique, the study administered pre-assessment and post-assessment tests to evaluate students’ learning difficulties in Mathematics. The results showed that the use of contextualized and localized instructional materials and worktexts significantly improved students’ performance, with notable enhancements in their understanding and application of mathematical concepts across all numeracy levels. A strong positive correlation was found between pre-test and post-test scores, indicating the effectiveness of these materials in improving mathematical comprehension and skills. The study underscores the importance of building on existing knowledge and skills in Mathematics education and provides insights into the development of effective instructional resources and strategies that address learners’ needs. These findings have implications for Mathematics instruction, highlighting the necessity of targeted support to strengthen foundational numeracy and foster deeper conceptual understanding. Overall, the results suggest that contextualized and localized instructional materials are valuable tools for enhancing students’ achievement in Mathematics.