President Donald Trump has proposed cutting after-school programs for young children, as well as grants and federal work-study programs for college students. But his most significant attack on public education may be his pledge to spend $20 billion on market-based school choice, including charter schools and vouchers.

Conventional voucher policies now exist in 16 states. Taxpayers in those states help pay private-school tuition for about 175,000 students each year. Education savings accounts that let states circumnavigate constitutional language against public funding for private and religious organizations are used in 17 states and generate another 250,000 vouchers annually.

Before the public embraces Trump’s plans to create even more vouchers, there are important things it should know about the voucher concept’s origination.

Milton Friedman, a University of Chicago economist and apostle of free-market fundamentalism, believed corporations should be able to profit from education. In 1997, he wrote an article arguing that vouchers were “a means to make a transition from a government to a market system,” to enable “a private, for-profit industry to develop” and ultimately abolish public schools.

(Next page: “Little evidence” of vouchers’ positive impact)