Many social, cognitive, emotional, and motivational aspects intervene in promoting children's well-being at school, or, conversely, in affecting their distress. It is, therefore, paramount to implement interventions addressing them in the classrooms. A workshop based on Social Theatre activities is proposed, with the aim of improving relational and emotional comfort by reducing bullying and bystanding behavior and increasing defending behavior and emotion regulation. The sample included 96 children (51 girls, mean age: 7.75 years), who were randomly assigned to an experimental group (EG, n = 49, two classes) and a control group (CG, n = 47, two classes). The EG participated in a 4-month theatrical workshop, in which games and exercises were proposed to work on poetry, improvisation, and to create small plays and a final performance. The CG did not participate in any activity. Questionnaires were administered to both groups before (T1) and after (T2) the workshop to assess bullying-related behaviors (bullying, victimization, outsider behavior, and defending behavior; students' self-reports) and emotion regulation and lability/negativity (Emotion Regulation Checklist; teachers' version). Results showed that the workshop contributed, although modestly, to stable emotion regulation and to reduce outsider behavior in boys. In addition, a decrease of emotion regulation in the CG was associated with an increase of outsider behavior at T2. Although further studies are needed, these findings are promising in demonstrating the effectiveness of the Social Theatre workshop for improving well-being at school.