According to the Wall Street Journal, school vouchers allow students to take tax money that normally goes to their public school and use that money to pay for private school instead. Time explains that these "school choice" programs are usually aimed at low-income students, since their families are less likely to have the extra funds to pay for a private education. This shrinks the gap between rich and poor students.
Parents of students who are in failing public schools, but lack the resources to send their child anywhere better, can often sign up for these programs. Depending on the state, the family can receive a voucher to pay for private tuition at a better school. This way, these students are no longer stuck at a poor performing school just because they cannot afford to go to a better one. School choice has been shown to increase parent satisfaction with their child's education.
Those opposed to school vouchers claim that these programs make poor schools poorer by taking the best students away, along with the money the schools would have received in order to educate those students. However, Time states that neither of these claims have proven to be true in districts that use vouchers.