The purpose of this study is to investigate the effects of game-based learning on year-nine students’ mathematics performance on the topic of ratios, rates, and proportions. This action research study consists of two cycles conducted in a public middle school in Brunei Darussalam. Cycle one is implemented in a class of seventeen students from Class A, and cycle two involves fourteen students from Class B. Both classes consist of year-nine average and lower-ability students. Tic-tac-toe has been chosen as the base design for the lesson intervention in this study due to its simplicity and flexibility. A similar achievement test was designed and utilized in both the pre-test and post-test. Students’ perceptions of the tic-tac-toe game were also studied through a four-point agreement Likert scale questionnaire and interview results. The findings showed that there was a significant increase in test scores from pre-test to post-test for both Class A and Class B, which indicates that the tic-tac-toe game has a positive effect on students’ performance in ratios, rates, and proportions. This study suggests that tic-tac-toe encourages critical thinking, promotes communication skills, and constructs an interactive learning environment for students.