Modified Project Summary/Abstract Section Drinking water instead of sugar-sweetened beverage (SSBs) can help prevent obesity and dental caries, two of the most prevalent pediatric diseases, disproportionately impacting marginalized youth. Adequate hydration also impacts cognitive function, essential for academic success. Federal policies require public schools to provide free drinking water and place restrictions on SSB availability. Yet, these policies alone have not optimized student hydration practices and numerous barriers to healthy hydration remain. An urban Virginia school district has partnered with our team to optimize hydration. This district has newly installed water bottle refill stations (“hydration stations”) and a model hydration policy. Yet challenges with policy implementation and inadequate drinking vessel access presented major barriers to hydration. To address this concern, we used a participatory approach to build capacity and gather in-depth information on community strengths and needs related to hydration. Grounded in participatory research methods and informed by extensive formative work, we developed a multi-faceted program that aligns with the social-ecological framework to optimize hydration, builds on district strengths, and addresses gaps. We propose to conduct a stepped wedge, cluster randomized controlled trial to test the effectiveness of the intervention within 12 randomly selected, matched Title I elementary schools serving predominately Black and Latino students from lower income backgrounds who all receive free meals (N=~6400 students). This intervention was designed collaboratively with key stakeholders, partners with teacher and student ambassadors, and includes social marketing, behavioral reinforcement, and education and outreach. Students and staff receive refillable water bottles and promotional materials encouraging water consumption over SSBs. Teachers receive training on the hydration policy and hydration lessons to integrate into their curriculum. School-wide assessments of: 1) hydration station usage (primary outcome), 2) water bottle usage and beverage selection at lunch, and 3) beverage intake will be conducted. Longitudinal assessments of anthropometrics and dental caries will be conducted with a randomly selected subset of 3rd grade students (N=406). We will also obtain data on beverage sales, NSLP participation, and academic outcomes, and conduct a systematic evaluation of sustainability. Consistent with the stepped wedge design, concurrent assessments will be conducted at 6 timepoints in all 12 schools over 3 years, with all baseline (T0 [timepoints prior to the intervention]) and post (T1-T6 [timepoints after receiving the intervention]) data used in primary effectiveness analyses. Results will directly inform school-based interventions addressing these urgent public health needs and guide policy mandates regarding access to and promotion of water within the school setting.