<![CDATA[This study aims to analyze the effect of ethnomathematics-based learning through the traditional Galah Asin game on students’ mathematical problem-solving ability in geometry, focusing on rectangles and relationships between lines (parallel and perpendicular), including area, perimeter, and partitioning of plane figures. The study employed a quantitative approach with a quasi-experimental method using a nonequivalent control group design. The participants were fourth-grade students from a public elementary school in Serang City, divided into an experimental class and a control class, each consisting of 41 students. The experimental class received ethnomathematics-based instruction through the Galah Asin game, while the control class received conventional instruction. The research instrument was an essay-based mathematical problem-solving test developed according to Polya’s problem-solving stages. Data were collected through pretest and posttest and analyzed descriptively and inferentially using an independent samples t-test, normalized gain (N-Gain), and Cohen’s d effect size. The pretest results indicated no significant difference in initial ability between the experimental and control classes (t = −0.711; p = 0.479), whereas the posttest results showed a significant difference (t = −17.755; p < 0.001). The experimental class achieved an average N-Gain of 0.71 (high category), while the control class obtained 0.39 (moderate category). The Cohen’s d value of 3.92 indicates a very large effect. These findings imply that integrating ethnomathematics through traditional games is a viable strategy for teaching geometry to enhance problem-solving ability, as it helps students understand concepts of area, perimeter, and relationships between parallel and perpendicular lines through meaningful real-life contexts.]]>
