Strategic Intervention Material (SIM) was found to play an effective role in bridging learning gaps in Science by focusing on those competencies that students have mastered the least. However, no studies have been found on strategic intervention materials integrated with game-based learning in Science education. This study aimed to develop and evaluate the effectiveness of Game-Based Strategic Intervention Material (G-SIM) in improving students' learning proficiency in Force, Motion, and Energy (FME), particularly in the identified least mastered competency. A quasi-experimental design was used in this study, specifically a one-group pretest-posttest design, since no comparison group was involved. The class was selected using purposive sampling and the respondents were obtained through total enumeration. A researcher-made 15-item pretest-posttest and an adapted 10-item perception survey were validated and used to gather data for one class of Grade 8 students (N= 37) in School Year 2025-2026 from a public secondary school in Tacloban City. Descriptive statistics and paired sample t-test were used to analyze the data. The results revealed that the posttest mean score (M= 10.86, SD= 2.08) was considerably higher than the pretest (M= 8.43, SD= 1.99). The use of G-SIM was statistically significant in improving the learning proficiency of the learners in the identified least mastered competency in FME, t(36)= 10.68, p< .001. Also, the learners expressed a very high perception of the effectiveness of using G-SIM (M= 3.47, SD= 0.57). This study implies that G-SIM is effective as an instructional method in improving learning proficiency in FME. Further investigations on the effectiveness of G-SIM in improving learning competencies in Science and other subjects are recommended.