Handwashing with soap is a critical preventive behaviour for reducing infectious disease transmission among school-aged children. Despite awareness of its importance, many children demonstrate inadequate handwashing techniques, reflecting limited procedural skill acquisition. Educational strategies that emphasize skill-based learning and engage multiple sensory modalities may be more effective, particularly for younger elementary school students. This study evaluated the effect of multisensory audio-visual education on observed handwashing skills among second-grade elementary school children. Methods: A cluster quasi-experimental pretest-posttest study with a control group was conducted among 200 second-grade elementary school students. Participants were allocated by classroom into intervention (n=100) and control (n=100) groups. Handwashing skills were assessed using a standardized observation checklist. Data were analyzed using generalized estimating equations (GEE) to examine the effects of group, time, and group-by-time interaction while accounting for repeated measurements. The findings indicate that baseline handwashing skills were comparable between groups. Following the intervention, the intervention group demonstrated substantial improvements in observed handwashing performance, whereas the control group showed only minimal changes. Generalized estimating equation analysis showed a significant group-by-time interaction (β = 27.60, SE = 2.90, p < 0.001), with a large intervention effect (Cohen's d = 1.45). Overall, multisensory audio-visual education effectively enhances handwashing skills among early elementary school children and supports its integration into school-based hygiene promotion programs.