The study investigated the influence of instructional materials on the performance of learners in mathematics at Comboni high school. The specific objectives included identifying the types of instructional materials available for teaching mathematics, examining whether these materials were utilized during instruction, and establishing the impact of their utilization on the development of mathematical competencies among students. Utilizing a survey research design, data were collected from a target population of 190 respondents, including head teachers, teachers, and students. A sample size of 150 participants was determined using Krejcie and Morgan's formula, employing simple random sampling for students and teachers, while school administrators were selected through criterion-based sampling. Primary data were gathered using structured questionnaires and interviews, while secondary data were sourced from school records. The findings revealed demographic characteristics, including a predominance of younger respondents and a gender distribution skewed toward males. Most respondents possessed only primary education, suggesting that limited educational qualifications may affect their engagement with instructional materials in mathematics. The results indicated the need for effective utilization of instructional materials to enhance mathematical performance among learners. The findings revealed that while textbooks and workbooks were the most accessible resources, the use of digital tools was limited. Although teachers incorporated various materials into lessons, their effectiveness was inconsistent, with only 51% of respondents strongly agreeing on their effective use. The study also highlighted that instructional materials significantly contributed to students' understanding of mathematical concepts and problem-solving skills. However, concerns regarding resource adequacy and the need for professional development were noted.