A prominent supporter of a market-based approach to improving public schools, Sol Stern, says he no longer believes charter schools or vouchers are a “panacea.”

In an article published in the latest edition of City Journal, Mr. Stern, a Manhattan Institute fellow, portrays the libertarian approach that once inspired him as a failed experiment, and urges those who agree with him to search for a “Plan B.”

The idea that what public schools need is not more money but more competition has become a major school of thought in education circles — “the dominant challenge in terms of big politics of school reform,” a professor of education and political science at Columbia University’s Teachers College, Jeffrey Henig, said.

Mr. Stern’s article appears to be the latest in a series of indications that its dominance is flagging.

“There’s a growing consensus that a market approach alone is not enough,” the president of the Albany-based Foundation for Education Reform and Accountability, Tom Carroll, said. He added: “There’s a need for a moment of reflection.”

The president of the Thomas B. Fordham Foundation in Washington, D.C., Chester Finn, who has been a vocal advocate of school vouchers and charter schools, said yesterday in an e-mail message that he has “growing sympathy” with Mr. Stern’s skepticism. Mr. Finn stoked debate himself recently by declaring that one factor hurting charter schools in Ohio is “too much trust in market forces.” He said his partial reversal is the subject of a memoir, “Troublemaker: A Personal History of School Reform Since Sputnik,” which will be released this year. Mr. Stern’s argument begins with his disillusionment with school vouchers, taxpayer-funded scholarships to private schools.

He writes that voucher programs were supposed to have a wide impact, helping not just the students who get scholarships, but also pressuring public schools to ramp up their quality in response — and pushing more states to create voucher programs.

Though students with scholarships have been helped, neither of the other outcomes has panned out, Mr. Stern says. A referendum in Utah recently was the latest voucher program to fail to win voter support, and in places where vouchers have passed, such as Milwaukee, Mr. Stern writes that the public school systems remain “miserable.”

“We can still hope that some legislature, somewhere in America, will vote for another voucher plan, or generous tuition tax credits,” Mr. Stern writes. “But does the school choice movement have a realistic Plan B for the millions of urban students who will remain stuck in terrible public schools?” In his article, Mr. Stern also takes on programs that use market approaches to try to fix public schools internally. He uses the New York City public schools under Mayor Bloomberg’s leadership as an example.

Saying there is no reason schools should not operate like the private sector, Mr. Bloomberg’s education department has introduced financial incentives for academic performance for everyone from students to teachers to principals. Mr. Stern, a vocal critic of the Bloomberg administration’s school policies, describes the programs as another market experiment that has not borne fruit, citing flat scores on a national test of student performance.

The executive director of the New York City-based advocacy group Democrats for Education Reform, Joseph Williams, called Mr. Stern’s description of newfound market competition unfair. “We’re still talking about the ultimate monopoly here,” he said of the public school system here.

But Mr. Williams said that if conservatives can sign onto the notion that the market is not a cure-all, Mr. Stern will have produced “a breakthrough moment.” Mr. Stern’s article describes a group of conservative scholars at a crossroads. He writes about a recent meeting of a task force of right-leaning scholars, the Koret Task Force on K-12 Education, during which a fissure opened up. One set of researchers stood firmly behind vouchers and charter schools, while another set, led by the writer E.D. Hirsch Jr., and the historian Diane Ravitch, declared that charter schools have produced “disappointing results.”

Mr. Henig, who is publishing a book about charter schools, said two developments might be behind the reconsideration.

First, he said, “we’re now deep into the choice era, and some of the promised benefits haven’t manifested themselves.”

Mr. Henig said politics may also be at play. As two terms of a Republican administration wind to a close, disagreements among conservatives that had been hidden are bound to break the surface, he said.

“It’s open turf,” he said. “It’s a more open arena for folks to try to craft a new message that will differentiate them and possibly put them in the lead in terms of where folks are going.”

Mr. Stern’s article offers one idea for a new direction.

Tying himself to a group he calls the “instructionists,” he declares that curriculum and pedagogy should be considered along with market solutions.

“The primal scene of all education reform is the classroom,” he writes. “If the teacher isn’t doing the right thing, all the cash incentives in the world won’t make a difference.”