<![CDATA[Elementary geometry is often difficult for students when instruction emphasizes formulas and procedures without sufficiently connecting geometric ideas to meaningful representations. This study developed and preliminarily evaluated an RME-based Betawi traditional house miniature as a culture-based manipulative for fourth-grade plane geometry. A Research and Development design using the ADDIE model was employed in a public elementary school in East Jakarta. The product was reviewed by one subject matter expert, three media experts, and three elementary education practitioners. An initial 30-item conceptual understanding test was piloted in Class IV-A; 25 items were retained for the classroom posttest. Class IV-B served as the experimental group and Class IV-C as the comparison group in a posttest-only, nonequivalent-group design. The product obtained a subject matter validity score of 96.7%, Aiken's V values of 0.88 from media experts and 0.93 from educational practitioners, and an overall student practicality score of 90.0%. The experimental group achieved a slightly higher posttest mean (M = 87.00, SD = 5.18) than the comparison group (M = 85.88, SD = 5.08), but the difference was not statistically significant, t(62) = 0.877, p = 0.384. The estimated effect was small and uncertain (Cohen's d = 0.219, 95% CI [-0.273, 0.710]). The findings support the validity and practicality of the developed medium, while evidence for superior learning outcomes remains inconclusive under the conditions of this study.]]>
