Data from the NICHD Study of Early Child Care and Youth Development (N = 723) were used to test whether the effects of fathers' supportive parenting on children's school readiness are greater when mothers are least supportive. We distinguished between academic and social dimensions of school readiness. Mothers' and fathers' parenting was assessed in dyadic parent-child videotaped sessions during the preschool period. Results for both academic and social outcomes indicated that fathers' supportiveness had larger benefits for children at lower levels of mothers' supportiveness. In fact, fathers' supportiveness was associated with children's school readiness only when mothers scored average or below on supportiveness. Mothers' supportiveness was similarly associated with children's social school readiness when fathers scored average or below on supportiveness. However, mothers' supportiveness was associated with children's academic school readiness even when fathers scored above average on supportiveness. The results suggest that fathers may influence child development most as potential buffers against unsupportive mother parenting. Further research is needed to replicate these analyses in a less socioeconomically advantaged sample. 2010 APA, all rights reserved