This study looks at the impact of using a voucher on college enrollments and on degree attainment. The data covers a span of 21 years, which allows the ability to record college enrollment and attainment up to seven years after a student's anticipated date of high-school graduation and observe students' college-going behavior even if their education was interrupted. The analysis includes 2,634 students: a "treatment" group of 1,356 who received an offer of a voucher and a "control" group of 1,278 students who did not. The analysis considers enrollment and degree attainment at both two-year and four-year schools. The authors look at the impact of the voucher program in two ways: (1) the effect of being offered a voucher, whether it was ever used; and (2) the effect of actually using the voucher to attend a private school for some period of time. The authors find large differences in impacts between moderately and severely disadvantaged students. An offer of a voucher has no detectable benefit for severely disadvantaged students--minority students from either extremely low-income households or whose mothers did not enroll in college. However, for minority students who are either from a moderately low-income household or whose mother has attended college, being offered a voucher increases college-enrollment rates by about 15 percent and four-year degree attainment by about 50 percent. Those impacts are even larger if students use the voucher to enroll in a private school. The findings point to the limitations of half-tuition vouchers to promote college enrollment and graduation among the least advantaged students, as well as their potential value for those with access to greater fiscal and cultural resources.