Early externalizing behaviors can have significant and persistent impacts on young children's developmental trajectories (Campbell, 1994; 1995; Moffitt, 1993). High-quality teacher-child relationships have the potential to protect children living in high-risk family environments from developing externalizing behaviors. Using Bronfenbrenner's bioecological framework, the current study explored the impact of family risks and teacher-child relationship quality on children's externalizing behaviors. Specifically, the goals of the study were to: (a) investigate the associations between family risk factors and children's externalizing behaviors, (b) examine the associations between teacher-child relationship quality and children's externalizing behaviors, (c) examine whether teacher-child relationship quality moderates the impact of family risk on children's externalizing behaviors, and (d) investigate the associations among teacher, student, and classroom characteristics and teacher-child relationship quality. Data were gathered from 100 Head Start children, their parents, and their teachers. Controlling for children's age and gender, results revealed that two family risk factors, parent-child dysfunctional interaction and family cohesion, significantly predicted child noncompliance. All of the teacher-child relationship quality variables including conflict, cohesion, dependency, and positive interactions significantly predicted children's externalizing behaviors, with conflict being the strongest and most consistent predictor. Finally, analyses on the interactions between the family risk and teacher-child relationship quality variables revealed that teacher-child conflict moderated the impact of family cohesion on child noncompliance. This finding suggested that low teacher-child conflict protects children from the impact of low family cohesion on child noncompliance, and high teacher-child conflict intensifies the impact of low family cohesion on child noncompliance. Overall, the results from this study suggest that teacher-child relationship quality may serve as both a risk and protective factor in the development of young children's externalizing behaviors. The findings presented have important implications for researchers, practitioners, and policy makers in understanding how to strengthen teacher-child relationships as a means to promote Head Start children's competence in the behavioral domain. (author abstract)