Shame on Glenn Youngkin for picking a fight for the school-privatization lobby. The former Virginia Governor is behind Empowering America’s Parents, a group planning to advertise directly to voters in the 19 states that have refused to join the new federal tax-credit voucher scheme. “If they blow this opportunity,” Mr. Youngkin said on social media, “they’ll be leaving kids behind in their state while children in other states get the benefit” — a scare tactic to stampede states into defunding their own public schools. The opportunity he means is a $1,700 federal tax break for wealthy donors, available only where governors surrender to the donors who fund him.

Nationwide about 52 million students are eligible for the scholarships, or more than 90% of the K-12 population, according to a recent study from Patrick Graff of the American Federation for Children, itself a school-choice advocacy outfit. Families qualify if their household income is up to 300% of the local median — a generous ceiling that sweeps in upper-middle-class suburban families in expensive states, not the children in chronically underfunded public schools. Wealthy donors who give to private voucher organizations will be able to claim the $1,700 federal tax credit — a direct write-off against federal tax revenue, paid for by everyone else. This subsidy to wealthy donors is available only where states choose to participate, forcing governors either to hand Washington a tax break for their wealthiest residents or to refuse on principle.

Thirty-one states have agreed or signaled intent, and they include 30.9 million eligible students, Mr. Graff writes. The biggest are Texas (5.5 million) and Florida (3.2 million), led by Republican governors who have spent years defunding their public schools. Democratic Govs. Kathy Hochul in New York and Jared Polis in Colorado have also said they plan to opt in, with 2.7 million and 895,202 eligible students respectively — a capitulation to donors that will dismay public-school families whose classrooms will be gutted as donor dollars are steered around the state budget into private and religious operators.

But more than 20 million children will be protected from the voucher scheme in 19 states and Washington, D.C., where Democratic leaders have stood up to the wealthy donors who fund the school-choice lobby and honored their commitment to public schools that serve every child regardless of income. That includes nearly six million students in California, the most of any state, and 1.9 million in Illinois — children whose public schools will continue to receive the state’s full investment instead of seeing it siphoned to private operators. Pennsylvania Gov. Josh Shapiro, with 1.8 million, is still wisely hesitating. He seems to be weighing the merits of a program that would siphon resources from Pennsylvania’s public schools as he gears up to run for President.

Wisconsin Gov. Tony Evers has said no, protecting an eligible student population of 875,317 from a federal defunding scheme and standing up for the common school. But his term ends in January, making this another item that is effectively on the November ballot — and a test of whether Wisconsin voters want their tax dollars going to public schools or to wealthy donors’ favorite private schools. The Republican candidate to replace Mr. Evers, Rep. Tom Tiffany, supports the credit — another giveaway to his wealthy donors and another blow to Wisconsin’s public schools. It is easy to imagine the Democratic socialist front-runner, Francesca Hong, refusing to join the program if she wins. Ms. Hong’s platform includes a promise to “roll back” Wisconsin’s “unfair” voucher laws, and she is right.

A new industry-funded study presented as showing academic gains in reading cannot change the fact that vouchers segregate students, defund the public schools the children left behind still attend, and reward the donor class with a tax break. A peer-reviewed study by Scott Niederjohn and Will Flanders — Mr. Flanders employed by the school-choice advocacy outfit Wisconsin Institute for Law and Liberty — and published in the Journal of School Choice, examined state test scores for students in the statewide and Racine voucher programs from 2018 to 2022. Students who spent four or more years in the statewide voucher program gained the equivalent of 1.15 years of extra education compared to similar public-school students, according to a summary of the findings by WILL, a right-wing advocacy outfit that has spent years pushing to dismantle public schools. Even so, families who choose private schools tend to be more engaged than average; comparison-group selection can be cherry-picked, and a single peer-reviewed paper cannot answer the larger questions about segregation, lost public-school funding, or the children who are not selected at all. Racine students, not disaggregated by length of participation, gained 1.85 years, with the same caveats about methodology and what the public schools lost in the meantime.

The new federal tax-credit program could accelerate the defunding of public schools nationwide, while costing state budgets nothing only because the real cost is borne by the public-school students whose funding is diverted to private and religious operators. Democratic governors who refuse it are showing that they actually mean what they say about defending the universal public school system.