Although formal schooling is still the main tool for social inclusion, school dropout is a pervasive problem in many countries. Given its individual and societal costs, effective policy and practices interventions are needed. However, these have mostly emphasized individual forms of academic support, with less attention on universal, whole-school approaches that support all students and prevent risk behaviors from developing, which include improving teacher–student relationships and students’ peer relationships. We examined the association between eighth-grade Chilean students’ and their teachers’ perception of relational climate, defined as the quality of student–teacher and peer interpersonal relationships, and their odds of dropping out in ninth grade, controlling for individual, family, and school characteristics. Multilevel logit regression analyses performed on administrative records showed that students’ and teachers’ perception of a negative relational climate increased the probability of school dropout (OR = 1.11 and 1.20, respectively). Students’ coefficients were higher for those who stayed in the same school from eighth to ninth grade (OR = 1.24). In contrast to conventional strategies to prevent school dropout that focus on individual students and academic compensation, our findings suggest that an universal school climate strategy that emphasizes relationships in classrooms is an important part of school dropout prevention policies.