Many empirical studies have established that financial aid improves college attainment. Few have been able to test why. This study used administrative records of employment and earnings to get a more complete picture of students' finances during college and test one potential mechanism, that financial aid buys students time by allowing them to work less in off-campus jobs. We studied recipients of New Jersey's need-based Tuition Aid Grant (TAG). We used the eligibility cutoffs of TAG to identify groups of otherwise similar students who received sharply different amounts of aid. A prior study took the same approach and found that TAG increased on-time graduation rates from public universities. At these schools, 80% of TAG recipients worked at some point during the year. We found that when students received additional aid, on average they reduced earnings dollar for dollar.