Employment, another common use of out-of-school time among adolescents, has been found to be predictive of academic achievement. A substantial number of studies have demonstrated a negative relationship between working over 20 hours per week and adolescents' academic achievement. Steinberg and Cauffman (1995) reviewed several studies that examined the relationship between adolescent employment and their educational development. The authors found that work intensity was the most consistently predictive employment variable for educational outcomes among adolescents. Generally, they found that working over 20 hours per week was associated with diminished school performance, as measured by grades or school engagement variables (Steinberg and Cauffman, 1995). Likewise, Jordan and Nettles (1999), in using NELS data, found that the number of hours adolescents worked in the 10th grade was negatively associated with their math and science test scores in the 12th grade after accounting for their prior achievement, background factors, such as race, SES, and family structure, and school-level factors.

Singh (1998) also found a negative relationship between academic achievement and adolescent employment, with students working longer hours being more likely to have lower grades and achievement scores than adolescents working fewer hours. Similarly, in an analysis of High School and Beyond data on a sample of 10,613 for whom data were assessed for both 10th and 12th grades, Marsh (1991c) found hours of work in the 10th grade predicted lower academic achievement, as measured by placement in academic track, grades, and test scores in the 12th grade. These findings remained constant after controlling for background factors, such as race, gender, and SES. Oettinger (1999), in a cross-sectional analysis of a sample of 2,510 11th and 12th graders using data from the National Longitudinal Survey of Youth of 1979 (NLSY), found that working longer hours during high school seems to was related more strongly to lower grade point averages for minority students than for students in other racial and ethnic groups. These findings held after controlling for individual and background factors, including number of siblings, race, gender, maternal education, and AFQT score, and history of grade repetition. However, one study found that working did not adversely affect grades. Warren, LePore, and Mare (2000), in an analysis of NELS data, found that preexisting differences between adolescents who work more and less intensely account fully for the relationship between work intensity and grades. With one exception, studies have consistently found that adolescents who work longer hours during the school year are more likely to have lower levels of achievement.

However, adolescents' employment during the summer months seems to have different implications for their achievement. For example, Oettinger, using cross-sectional data, found no relationship between adolescents' summer employment and their GPA. However, Marsh (1991b), in a longitudinal analysis, found that summer employment was related to higher levels of achievement, after controlling for school-year employment and background factors.