between high-intensity work in high school and lowered eventual educational attainment.
Although there is much concern about whether working lowers students' academic performance, the evidence with respect to this outcome is inconsistent. Some well-designed longitudinal studies report negative effects of employment, or hours of work, on grades (Marsh, 1991; Mortimer and Finch, 1986). Others show no significant effects (Mihalic and Elliot, 1997; Mortimer and Johnson, 1998; Mortimer et al., 1996; Schoenhals et al., 1977). Parents also have reported that their children's work has not affected their grades (Phillips and Sandstrom, 1990). Steinberg and colleagues' (1993) longitudinal assessment of change in grade-point average, considered as an outcome of employment, yielded mixed findings. Students who worked at low intensity (defined as 1–20 hours per week) at the outset of the study and increased their hours to more than 20 per week had lower grades at the end of a 1-year interval than students who worked at low intensity and left the work force during this period. Among students who worked more than 20 hours at the outset of the study, those who stopped working increased their level of school engagement. The results of this study cannot be generalized as the sample was not representative, but they do suggest the need for researchers to examine the effects of patterns of work intensity over time.
It is important to note that the dividing point of 20 hours of work per week is not based on research results; rather, most researchers have adopted that number as a reasonable marker between ''low-intensity" and "high-intensity" employment. Given an average school week of about 30 hours, students who work 20 hours per week during the school year have the equivalent of a 50-hour work week. Surveys often collect hours worked in 5-or 10-hour groups, precluding researchers from examining hours of work as a continuous variable. Furthermore, the number of hours worked per week does not take account of when those hours are worked, either on what days of the week or what times of the day, both of which may affect the effects of work on school outcomes.
It is plausible to assume that the motivational context and social meanings of employment influence its effects on academic performance. For example, Marsh (1991) and Ruscoe and colleagues (1996) report that employment has a beneficial effect on grades when the workers are using their earnings to save for college. (In the