This paper studies how receiving a customized signal of ability affects individuals’ educational investments. In 2013, students who took the Preliminary SAT received a message in their results report that signaled their potential to succeed in Advanced Placement (AP) coursework based on their test scores. Survey data from students in the Oakland Unified School District revealed that the signal had informational value, leading students to revise their selfassessed academic ability and plans for AP enrollment, consistent with Bayesian learning. Using a regression discontinuity design, I found that the signal increased the probability of participating in AP classes by 49 percentage points among surveyed students, leading them to enroll in and pass about one more AP course the following year compared to students who did not receive the signal. However, students who were not surveyed for the study did not respond to the signal. The results suggest that ability signals can be a cost-effective way to increase educational investments, but may only work when they are made salient.