We examine how changes in maternal work hours affect adolescent children's school participation and performance outcomes using data from interviews in 1998 and 2001 with 1,700 women who in May 1995 were welfare-reliant, single mothers of adolescents living in disadvantaged neighborhoods in four urban counties. We find unfavorable effects of maternal work hours on several aspects of adolescents' schooling: Full-time maternal employment (31 hours or more per week) increases the likelihood of skipping school, decreases school performance, and increases the likelihood of parent contact by a school about behavior problems. Sons seem to be particularly sensitive to changes in mothers' average hours of work, with notable increases in incidences of being late for school and declines in school performance when mothers work more hours. These findings hold up controlling for a rich array of mothers' characteristics, including their psychological and physical health and experiences with domestic violence and substance. Appended are: (1) Criteria to be Eligible for Cross-Sectional Analysis Sample; and (2) Comparison of Means for Wave 2 Analysis Sample and Children Excluded from Sample. (Contains 7 tables and 8 footnotes.)