The cost of attending college has risen steadily over the past 30 years, making financial aid an important determinant of college choice for many students and a subject of concern for colleges and state governments. In this paper, we estimate the effect of rule-based merit aid assignment on students' enrollment decisions at the University of Iowa. Iowa evaluates many students using an admissions score comprised of high school grade point average and class rank, core high school courses, and one's ACT test score. Students from out-of-state who meet a specific threshold score qualify for the National Scholars Award (NSA), presently worth nearly $20,000 over 4 years. We employ a regression discontinuity model to take advantage of award assignment criteria, finding that the award does increase the probability of enrollment at Iowa. This result is robust for several applicant subsamples and passes falsification checks using Iowa residents, who are ineligible for the award. Preliminary analysis of an earlier, tiered version of the currently single-valued award suggests that the NSA may have strong effects on very high-achieving candidates.