Even the most effective education reforms and initiatives are unlikely to have a uniform effect on all students. In fact, much like in medicine, some beneficial efforts can have adverse side effects. Yong Zhao takes up this idea as it applies to school choice and voucher programs. When researchers tout the benefits of vouchers, they focus on the average effect of such programs on participating students. But because some students experience negative effects, Zhao argues that vouchers must not be considered a panacea for improving student outcomes.