The teachers' unions blockade, which deprives poor children of good education, is starting to crack.

The latest fissures are created by a study of the country's largest private school choice program. According to researchers, the Florida Tax Credit Scholarship program, which provides vouchers, increased college enrollment rates by about 6 percentage points for students who participated at all. For those who were in the program for four or more years, the college enrollment rate was as much as 17 points higher.

Before anyone leaps to suggest that this really just means those schools cream off the best students, opponents of school choice should know that children in the program disproportionately come from families with low incomes and, before joining the program, were mostly at bad public schools and did poorly on tests.

The source of this new information is not what opponents might think of as one of the usual suspects. It was not some conservative think-tank, but the left-leaning Urban Institute, a think-tank founded by President Lyndon B. Johnson.

It won't change minds at the National Education Association or the American Federation of Teachers, of course, for nothing does that. But it is pleasing to be able to report that the teachers' unions may soon have less clout. This probability comes not from any new open-mindedness on education among their Democratic allies, but from the judicial system.

On Thursday, the Supreme Court agreed to hear a suit challenging a 1977 ruling that said public-sector unions may force non-union employees to pay for bargaining costs. Unions probably got lucky when Justice Antonin Scalia's death led to a 4-4 split in a 2016 case that made the same challenge. Now that Justice Neil Gorsuch is on the court, they seem unlikely to have the same luck.

Without a flood of plundered money, unions will be a diminished force, and their power over Democratic politicians will likewise decline. As polling increasingly shows bipartisan support for school choice, especially for the type of program in Florida, politicians are likely to swing that way too. They go where they can get votes.

Empirical data is convincing, but the strongest argument for school choice is one of principle. Parents, not the state, should decide what school is best for their child. Bureaucrat neither know nor, on the evidence of their failure over decades, care anything like so much.

There are 52 private school choice programs in 26 states and Washington serving 430,000 students. Nearly 3 million more students exercise a form of public school choice by attending charter schools. For the tens of millions of students who don't yet have any choice, especially those trapped in awful public schools, the end of the status quo can't come soon enough.