Psychosocial risk exposure in childhood is associated with a greater probability of emotional, behavioral, and academic problems. It is not surprising that children who experience homelessness, a marker of high cumulative risk, show significant emotional and behavioral problems and lower academic achievement than other children, including impoverished children who are not homeless. Nonetheless, some children manifest positive adjustment despite the hazards associated with homelessness, and it is important to identify protective influences that might be targeted for intervention. One potential factor is mastery motivation (MM), or the drive to control and master challenges, theoretically associated with resilience and empirically linked to adaptive cognitive outcomes in low-risk children. Currently, there is little research on MM in high-risk young children overall, and data are particularly limited on the key question of whether MM is associated with better outcomes in domains crucial for school readiness, including socioemotional adjustment, self-regulation, and academic competence. This study examined observed MM in 85 young children ages 3 to 5 living with their parents in an emergency shelter. Children completed behavioral tasks to assess MM, and measures linked with school readiness were assessed directly or by parent report. Higher MM was associated with better social and emotional functioning and emotion regulation but not math achievement or executive functioning. Follow-up analyses indicated that MM was indirectly associated with prosocial behavior through better emotion-regulation abilities. Implications are discussed for further research and for interventions designed to address educational disparities and promote school success for children experiencing homelessness. (author abstract)