Previous research on family structure and child development has largely focused on the disadvantages faced by children who transitioned out of married families. However, we know less about how family structure affects child outcomes for children starting out in single-mother families. In this article, we use the kindergarten cohort of the Early Childhood Longitudinal Study to analyse children’s academic outcomes between kindergarten and eighth grade. We found that living in single-mother or step-families was clearly associated with lower test scores for children starting kindergarten in married biological-parent families, but the same disadvantages associated with living outside a married biological-parent family structure were not found for children starting kindergarten in single-mother families. We also found preliminary evidence of a buffering effect of maternal education in the relationship between family structure and children’s academic outcomes.