Game-based learning instruction allows students to engage with educational games and strategic instructional materials in a playful and dynamic way. Kwatro is a mathematical card game designed to develop mastery of the computational skill of the students on the topics relative to addition of integers. A quasi-experimental pretest-posttest design was used to determine the effectiveness of the game Kwatro in improving the level of performance of the least performing students in Addition of Integers with twenty-five 7th-grade students from San Roque National High School, School Year 2021-2022. The instruments of the study consisted of a 20-item multiple choice teacher-made pre-posttest about addition of integers and card games. The results of the pre-test and post-test show an increase in the performance of students from DNME (Did Not Meet Expectation) to FS (Fairly Satisfactory) after the utilization of the game. The result of the t-test revealed that there is a significant difference between the pretest and posttest scores of the 25 students after the utilization of the game. This means that the utilization of Kwatro is effective in improving the level of performance of the least performing students in addition of integers. Kwatro can be used even in blended learning with teachers and parents’ supervision in times of pandemic.