The purpose of the study is to determine the effectiveness of Strategic Intervention Material (SIM) in intervening least learned competency – based skill in mathematics. Specifically, a one group pretest-posttest research design was utilized for the study. The sample consisted of fourteen (14) Grade 5 pupils were given remediation on the identified lowest least learned competency – based skill using researcher – made SIM. The 20 – item researcher – made questionnaire were used in collecting data of the study. The questionnaire was validated to determine its reliability. The reliability value of the questionnaire is 0.71. Results of the study revealed that there is a significant difference between the pretest (M=7.786) and posttest (M=15) scores of the respondents in the given topic using paired t-test at 0.05 level of significance. This implies that Strategic Intervention Material (SIM) is an effective strategy in intervening least learned competency – based skill in mathematics. Thus, teachers in mathematics are urged to use SIM in their respective classes to improve the performance of their pupils and intervene the least learned competencies.