Grant aid reduces the financial burden of human capital investment in postsecondary education. Theory suggests grant aid should substitute for other financial resources such as borrowing and labor market participation. Although studies have individually examined the impact of grant aid on hours of paid work and on borrowing for education, students make borrowing and work decisions jointly. By applying a regression discontinuity design to nationally representative data of students enrolled in four-year colleges, this study simultaneously identifies the substitution effects of exogenously received increases of grant aid on hours of paid labor, earnings, and borrowing. Results confirm students substitute grant aid for both paid labor and borrowing. An average increase of $1,100 in grant aid reduces weekly job hours by one and a half to two hours per week for women, corresponding to a decline in annual earnings of $850, and reduces borrowing by an average of $300-$400 dollars among all students. We find limited evidence of grant aid's impact on academic outcomes.