The authors explored the effects of part-time work on school achievement during high school. To estimate the true effects of part-time work on school grades, the authors included family background, students' educational aspirations, and school engagement as controls. Although a substantial literature exists on the relationship of part-time work and school achievement, the findings are inconsistent. The authors hypothesized that work intensity, as measured by number of work hours per week during the school year, would produce a negative effect on achievement. Results indicate that work hours do have a negative relationship with students' self-reported grades after controlling for family background, educational aspirations, and school-engagement. The authors also discuss practical implications of the findings. (Contains 5 tables and 2 figures.)