Vomiting and diarrhea are common symptoms in a myriad of pediatric illnesses. Both can lead to and/or worsen dehydration. Globally, diarrheal illness still accounts for a sizable proportion of pediatric mortality. In resource abundant countries, especially since the adoption of rotavirus vaccines into routine immunization schedule and attention to the sanitation of and access to safe drinking water, the mortality has significant improved. Despite this, morbidity and the burden of illness remains significant. This chapter will present three cases of acutely ill students, and discuss the initial evaluation, differential diagnosis, signs/symptoms necessitating additional medical attention, and disposition/return to school criteria (Cunningham et al., N Engl J Med 379:2468–2475, 2018; Diarrhoeal disease. World Health Organization, https://www.who.int/news-room/fact-sheets/detail/diarrhoeal-disease ).