If Donald Trump knew that promoting school choice would cause such a ruckus on the left, maybe he’d have weighed in sooner. The Republican nominee has found a winning issue by pitching a plan to “provide school choice to every disadvantaged student in America.” Amen.

During a visit to the Cleveland Arts and Social Sciences Academy, Mr. Trump proposed a $20 billion block grant for states by redirecting federal education money to support charter schools and vouchers. He also endorsed merit pay for teachers and said he’d support local candidates who champion school choice.

Most of the $50 billion or so that the federal government spends on K-12 education is targeted to particular programs like teacher training, and rural and STEM education. About $14 billion in Title I funds are earmarked for disadvantaged students. However, this money doesn’t follow kids to private schools, and states often shortchange charter schools.

Mr. Trump wants to let states use federal funds to boost voucher awards, so parents rather than governments get to choose where the money goes. As he noted in Cleveland, “there is no failed policy more in need of urgent change than our government-run education monopoly.” Judging by the panicky reaction on the left, you’d think he’d proposed eliminating public education.

Hillary Clinton said his block-grant plan would “decimate public schools across America.” Yet $20 billion is merely 3% of what states spend on K-12 education each year and less than the increase in school spending in California since 2012. By the way, charters are public schools—freed of union control.