Many undergraduates are placed onto academic probation at some point during their enrollment. Prior research findings are mixed on whether and when academic probation affects the likelihood of college graduation. The present study examined the impact of probationary placement on six-year graduation using regression discontinuity analyses overall and within several subgroups that have received little or no attention to date. Academic probation often led to sizable declines in the chances of graduation, especially when students were placed on probation as a result of low semester Grade Point Average (GPA). Transfer students exhibited especially adverse effects of probationary placement based on semester GPA. Academic probation based on overall GPA had sizable negative effects among students in their third or fourth year of college and among students who had previously been placed on probation at least once. Additional analyses indicated that roughly half of the impact of academic probation (based on both overall and semester GPA) on six-year graduation was driven by university attrition that occurred before students even started the semester in which they would be considered "on probation"; therefore, institutional efforts targeted toward the probationary semester would be too late to reach this group. Implications for policy, practice, research, and assessment are discussed.