Intensive handwashing promotion can reduce diarrheal and respiratory disease incidence. To determine whether less intensive, more scalable interventions can improve health, we evaluated a school-based handwashing program. We randomized 87 Chinese schools to usual practices: standard intervention (handwashing program) or expanded intervention (handwashing program, soap for school sinks, and peer hygiene monitors). We compared student absence rates, adjusting for cluster design. In control schools, children experienced a median 2.0 episodes (median 2.6 days) of absence per 100 student-weeks. In standard intervention schools, there were a median 1.2 episodes (P = 0.08) and 1.9 days (P = 0.14) of absence per 100 student-weeks. Children in expanded intervention schools experienced a median 1.2 episodes (P = 0.03) and 1.2 days (P = 0.03) of absence per 100 student-weeks. Provision of a large-scale handwashing promotion program and soap was associated with significantly reduced absenteeism. Similar programs could improve the health of children worldwide.