specifically socioeconomic status, family environment, and the respondent's ability and motivation toward school. The absence of information on the quality of the work prevented consideration of what could be an important factor in understanding the effects of work.

All of the analyses of the NLSY data have controlled for factors other than hours worked while in school in explaining the persistent benefits of work. Managing these confounding factors in statistical models is complex and the results may be difficult to interpret. Recently, the data from the NLSY were examined by Hotz and colleagues (1998), using econometric modeling to study the effects of working during school on future wages.2 When they controlled for person-specific unobserved heterogeneity (i.e., potential differences between subjects that were not measured), working during high school had no significant effects on wages at age 27. In fact, in this model, the effects of going to school full-time and not working appeared to have much bigger payoffs in terms of future wages than combining work and school.

Mortimer and Johnson (1998), using data from the St. Paul Youth Development Study, reported that long duration of work in high school was associated with being employed part-time during the 4 years after high school. Part-time employment after high school was, in turn, linked to enrollment in post-secondary education. They found that working more than 20 hours per week during high school predicted entry into full-time employment after high school. Working more than 20 hours per week and having a long duration of work during high school, for males only, was associated with higher earnings 4 years after high school than the earnings of those with less work experience during high school.

Though most research has focused on investment in work, the quality of the early work experience may also be important for occupational outcomes. For example, the use of skills as an adolescent worker predicts success in the job market during the first 3 years after high school graduation (Stern and Nakata, 1989).


Based on a framework developed by Cameron and Heckman (1992), which draws on earlier work by Heckman (1982) and Heckman and Singer (1984).

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