Since early January 2021, several children at an elementary school in Vaucluse have exhibited gastrointestinal and general symptoms across multiple classrooms. Given the ongoing COVID-19 pandemic, viral transmission within the school was suspected, but PCR test results came back negative. Initial environmental tests were also negative, ruling out the presence of CO in the school. An epidemiological investigation, including a questionnaire for affected students, was conducted in addition to the environmental investigation to identify the cause of this episode. A variety of symptoms were reported by 40 students, representing an attack rate of approximately 27% among the entire student body but significantly higher in first-grade classes (56%). The data collected during the investigations ruled out the hypothesis of chemical or infectious poisoning and led to a diagnosis of a mass psychosis with a strong emotional component in a locally anxiety-inducing context linked to the COVID-19 pandemic and the requirement for 5- to 11-year-olds to wear masks at school. This episode exhibited all the characteristics of the unexplained mass psychosis described in the literature. The management of symptomatic children within the school by the school health service helped reduce tensions and anxiety and gradually bring the situation under control.