PROJECT SUMMARY Proper hand washing is a cost-effective intervention that offers powerful protection against a host of gastrointestinal and respiratory transmissible diseases, but only if done effectively, at the appropriate time, and consistently. Global campaigns to increase handwashing have raised awareness, but significant barriers to improved handwashing remain. Teachers and parents are not commonly taught proper technique. As a result, despite massive, and costly installation of handwashing stations and signage, too often children do not use soap or sanitizer effectively—even with adult supervision. Beyond technique, students struggle to remember when to wash when occasions require it. Despite years of pandemic, heightened awareness, and sincere efforts by adults and children alike, durable handwashing habits have not taken hold. OBJECTIVE: We aim to create an interactive digital trainer that: 1) depicts hand anatomy correctly for more accurate learning; 2) provides an immersive educational experience, with critical visual feedback of germs remaining, so that students learn to use the appropriate scrub motion to address specific areas of that hand that were inadequately cleaned; 3) engages students to play again, over several sessions, to foster habit formation, and durable gains in hand hygiene. RESEARCH DESIGN: In Phase I, we successfully created an innovative, engaging, and highly entertaining prototype: the Bubble Beats handwashing trainer. We established that our technology works on Chromebooks, iOS devices, and PCs. After a single session with the trainer, students demonstrated a significant increase in World Health Organization (WHO) hand hygiene steps performed at the sink. In Phase II, we will develop a fully-featured solution, with supporting material for teachers, and test this product in an independent evaluation across multiple classrooms, in a randomized controlled trial. METHODS: AIM 1: PRODUCTION. Teacher co-developers, domain experts, and students will participate throughout the project in rapid and frequent cycles of design, build, test, and refine. Early usability testing with small groups will test new components of the trainer, for eventual integration into the completed product. We will evaluate the effectiveness of these new components assembled together in authentic classroom settings. Handwashing proficiency will be measured by photometric analysis of images of hands before and after washing, and video analysis of WHO scrub steps performed while washing at the sink. AIM 2: EVALUATION: Finally, a formal and independent evaluation across multiple classrooms will measure short- and long-term impacts of the training, to determine healthy habit formation for handwashing.