This study investigates whether there are differences in preschool children’s cognitive, social, and behavioral development in families where mothers work nonstandard hours (i.e. night, evening, rotating) compared to regular hours. We also explore the role maternal stress and depression may play in explaining children’s differences in cognitive and socioemotional development within single mother families. Multivariate hierarchical analyses were conducted on a national sample of preschool age children (four to five years) living in a single mother household using data from the Early Childhood Longitudinal Study- Birth Cohort (ECLS-B). Our results show that preschool children whose mothers worked nonstandard schedules had significantly lower cognitive, social and emotional development compared to children whose mothers worked the regular dayshift. These disparities persisted even after extensive controls including number of hours worked, maternal age and education, and child’s prior development at two years old. Surprisingly, we also found that externalizing behavior was not related to nonstandard work hours. Our findings highlight the need to further unpack the negative impact working nonstandard hours has on children’s early cognitive skills as well as socioemotional development in households headed by single mothers. (author abstract)