This study investigates how maternal employment is related to the cognitive development and body weight of 10 and 11 year olds, controlling for a wide variety of child, mother and family characteristics. The results suggest that limited market work benefits youths who are relatively "disadvantaged" and even long hours, which occur infrequently, are unlikely to leave them much worse off. By contrast, maternal labor supply is estimated to have more uniformly harmful consequences for "advantaged" adolescents. The negative cognitive effects for these youths probably partly occur because maternal labor supply reduces the time spent in enriching home environments. Some of the growth in obesity may be related to determinants of excess weight common to the child and mother.