Yesterday's broadly written Supreme Court ruling upholding a school choice program in Cleveland has been a long time coming. It was back in 1983 that the Education Department issued its "Nation at Risk" report warning of "a rising tide of mediocrity" in the schools. Two months later, the Supreme Court opened a first crack in the door of school choice when it declared that states could allow taxpayers with children in private schools to deduct tuition and other expenses from state income taxes. Yesterday's ruling represented the high court's final and complete retreat from the suspicion it once displayed towards school choice and the role religious schools can play in it.

As with its landmark Brown v. Board of Education ruling desegregating schools, the justices were clearly mindful of the grim reality that too many of the nation's public schools are failing to provide an adequate education for the most vulnerable children. A 50% increase in real (inflation-adjusted) spending per pupil in the last two decades has failed to deliver results. Since 1983, over 13 million children have reached the 12th grade not knowing how to read at a basic level. Over 27 million have reached their senior year unable to do basic math. And those numbers don't count the 30% of students who drop out of school before the 12th grade.

The court surprised many observers by writing a broadly written opinion that gathered the full support of five justices. Unlike in the Mitchell decision in 2000 that upheld the use of federal funds for public entities lending education materials to religious schools, Justice Sandra Day O'Connor did not dissent in part from yesterday's ruling upholding school choice. This means that the opinion can be used as binding case law. The canard that school choice programs are an impermissible breach of the wall of separation between church and state has now been exploded.

Indeed, the court's majority used its opinion to tweak the dissenting justices for their fear of school choice. In response to Justice Stephen Breyer's use of the specters of "divisiveness" and "religious strife" to bolster his view that Cleveland's choice program was unconstitutional, Chief Justice William Rehnquist wrote: "It is unclear exactly what sort of principle Justice Breyer has in mind, considering that the program has ignited no 'divisiveness' or 'strife' other than this litigation."

The court's ruling will have both practical and political effects. Jay Greene of the Manhattan Institute predicts the decision "will affect the tenor of education policy for years to come." There is little doubt it will embolden states such as Colorado and Texas to launch bolder school reforms, including targeted vouchers but also possibly tax credits and an expansion of charter schools. Other states may now modify or repeal their constitutions to strip out 19th century Blaine Amendments, which restrict aid to religious schools.

What the court's decision will not do is alter the implacable opposition of teachers unions to most forms of choice. In 2000, Robert Chanin, general counsel of the National Education Association, warned that no matter what the Supreme Court ruled, the union would challenge choice "on whatever grounds are available to us -- from lofty principles . . . to 'Mickey Mouse' procedural issues." Up to now, Mr. Chanin and his allies have been winning.

Minority voters are the most supportive of private options in education, but most won't vote for candidates on that basis, limiting the appeal of the issue to conservative politicians. Meanwhile, many suburban voters remain ignorant of school choice, complacently believing their local schools are wonderful or falsely fearing the changes that school choice could bring.

But targeted school choice programs should nevertheless flourish. Today, almost every state uses public funds to send special-education students to private schools if the public schools can't address their needs. A dozen states will, at the request of principals, transfer disruptive students to private schools with strict disciplinary programs. Expanding those programs could be popular, and could force public schools to improve their own performance to compete.

"Candidates of all kinds will be much more willing to talk about dramatic school reform such as the Bush proposal to give families tax credits if they feel compelled to leave a failing public school," says Ralph Reed, chairman of Georgia's Republican Party. In intellectual circles one can expect to see some strange new respect for the lonely band that championed school choice before it was cool: the Bradley and Olin Foundations, the Milton Friedman Foundation, the Institute for Justice, businessman Pat Rooney and former Milwaukee School Superintendent Howard Fuller.

The education establishment, which Bill Bennett once called the "blob," still dominates the political arena. But yesterday's decision makes its hold on power a little more tenuous.