This study examined teacher-child conflict as a possible mediator of the effects of temperamental anger and effortful control on subsequent externalizing behavior. Reciprocal influences between teacher-child conflict and externalizing behavior were also examined. Participants were 1,152 children (49% female; 81.6% non-Hispanic White) from the Study of Early Child Care and Youth Development. Multivariate growth curve modeling revealed that greater effortful control at age 54 months indirectly predicted lower levels of, and subsequent changes in, externalizing behavior from kindergarten to Grade 6 through reduced teacher-child conflict. An alternative model, in which greater effortful control predicted lower teacher-child conflict through lower externalizing behavior, received less support. Within persons, greater-than-expected teacher-child conflict predicted greater-than-expected teacher-reported externalizing behavior concurrently and over time.