This longitudinal study examined adolescents' mental health, academic achievement, and behavioral adjustment in relation to work intensity during high school. Data were collected from approximately 1,000 adolescents during a 4-year period, beginning in the subjects' freshman year of high school. Self-administered questionnaires were distributed each year; 93 percent participation was maintained over the 4-year period. Mental health variables measured included depressive affect, self-esteem, and mastery orientation; two indicators of school achievement were grade point average and time spent doing homework. Adolescents were considered employed if they were working at least once a week outside their home for pay at the time of each survey. Work intensity was measured by hours of employment per week. Analysis showed that 12th grade students who worked fewer than 20 hours per week had significantly higher grade point averages than students who did not work at all. Only in the senior year did students who worked long hours spend less time on homework. No evidence to support the claim that working long hours fosters smoking or school problem behavior was found. However, there was evidence that as work hours increased, alcohol use also rose. No significant relationships between hours of work, psychological outcomes, and indicators of school involvement were found. (MM)