Research Findings: Racial/ethnic minority low-income children with temperaments high in negative reactivity are at heightened risk for developing disruptive behavior problems. Teacher-child relationships characterized by high levels of closeness and low levels of conflict may protect against the development of disruptive behaviors in school. The present study examined whether teacher-child closeness and conflict moderated the association between temperamental negative reactivity and growth in disruptive behaviors in low-income Black and Hispanic kindergarten and 1st-grade children. Findings revealed that negative reactivity predicted higher overall levels of in-school disruptive behavior problems at the beginning of kindergarten as well as growth in behavior problems over kindergarten and 1st grade. However, the effect of negative reactivity on disruptive behaviors was attenuated when children had relationships with teachers characterized by high levels of closeness and low levels of conflict. Practice or Policy: Implications for further research and practice are discussed.