Testing aids, including student-prepared testing aids (a.k.a., cheat sheets or crib notes) and open-textbook exams, are common practice in post-secondary assessment. There is a considerable amount of published research that discusses and investigates the impact of these testing aids. However, the findings of this research are contradictory and inconclusive. The current meta-analytic investigation provides a general measure of the impact of both student-prepared testing aids and the use of open-textbook exams on student exam performance in post-secondary education, while examining variables that may moderate the effects of testing aids on student exam performance. The results indicate that, overall, testing aids can produce a moderate impact on student exam performance, with student-prepared testing aids associated with a larger effect (d = 0.402) relative to open-textbook exams (d = 0.257). The results are discussed in terms of their implications for college course instructors and for informing the broader debate about the role of testing aids in long-term student learning and mastery of course material.