Guidance counselors provide the main source of college advising for low-income high school students, but are woefully understaffed in high-need schools. This paper evaluates an approach to school-based college advising that relies on teachers rather than counselors. Using a randomized control trial in sixty-two Michigan high schools, I estimate the effects of a college planning course for high school seniors on postsecondary enrollment, persistence, and degree receipt. The course teaches about postsecondary education opportunities, application processes, and strategies for persisting toward a degree. I find no effect of the course on the number of students entering college, but an increase in the number persisting and earning a degree, particularly among low-income students. This is due to a shift in the composition of enrollees toward higher-achieving students: the course increases enrollment among high-achieving, low-income students, who have relatively high persistence rates, and reduces enrollment among low-achieving students, who in the course's absence would have enrolled and then quickly dropped out. The program's main cost is potential learning loss from displaced time in other subjects, which is difficult to measure but appears small.