Social-emotional competencies (SECs) stand to benefit children in a myriad of ways. However, school-based social-emotional learning (SEL) programs are often ineffective in low-income, urban school districts, calling into question whether they adequately address student needs. The present study investigated whether and how one source of stress more common in these communities--school mobility--impacted SEL for predominantly African American students living in a low-income, urban district. Using a series of multi-level growth models, we found that school mobility was only detrimental (on average) under certain circumstances--for example, when students moved to schools with worse relative levels of school safety. These findings suggest that SEL programs should address school climate and safety in addition to individual-level competencies.