This study examined the relation between part-time employment and adolescent behavior and development in a multi-ethnic, multi-class sample of approximately 4,000 15- through 18-year-olds. The results indicated that long work hours during the school year were associated with diminished investment in schooling and lowered school performance, increased psychological distress and somatic complaints, higher rates of drug and alcohol use, higher rates of delinquency, and greater autonomy from parental control. Workers did not have any advantages over nonworkers with respect to self-reliance, work orientation, or self-esteem. The correlates of school-year employment were closely linked to the number of hours worked each week and generally cut across ethnic, socioeconomic, and age groups, although the association between hours of employment and poor school performance was clearer among White and Asian-American adolescents than their peers. Nevertheless, in no ethnic or socioeconomic group were the correlates of employment positive, either in terms of lower rates of dysfunctional behavior, better school performance, or enhanced psychosocial well-being. These and similar findings from previous research suggest that parents, educational practitioners, and policy-makers should continue to monitor the number of weekly hours adolescents work during the school year. (Author)