Studies of the competition effects from voucher or tuition tax credit scholarship programs on public school student academic outcomes have taken place in seven locations throughout the United States, with the majority of studies taking place in Florida, followed by Wisconsin. This article reviews 21 total studies of the impacts on student academic outcomes, finding neutral to positive results. The various competition measures used in the literature are thoroughly reviewed and regression discontinuity design is identified as the most rigorous estimation strategy capable of identifying the causal effect of competition threats on traditional public schools.