Even some groups that share her support for charter schools worried that picking someone so closely identified as a champion of vouchers signaled that the Trump administration would try to starve public schools.

As a candidate, Mr. Trump proposed steering $20 billion in existing federal money toward vouchers that families could use to help pay for private or parochial schools, perhaps tapping into $15 billion in so-called Title I money that goes to schools that serve the country’s poorest children. He called school choice “the civil rights issues of our time.”

Image Betsy DeVos, the pick for secretary of education, has advocated charter schools and vouchers. Credit Drew Angerer/Getty Images

Amber Arellano, the executive director of the Education Trust-Midwest, an advocacy group in Michigan that supports charters but has been critical of a Michigan charter school law that Ms. DeVos has spent millions to defend, said the pick had “the potential to undermine the nation’s hard-won progress by diverting resources from the young people who most need them, or by failing to uphold the federal government’s responsibility to protecting the needs and interests of all students — especially the most vulnerable.”

Michigan is one of the nation’s biggest school choice laboratories, especially with charter schools. The Detroit, Flint and Grand Rapids school districts have among the nation’s 10 largest shares of students in charters, and the state sends $1 billion in education funding to charters annually. Of those schools, 80 percent are run by for-profit organizations, a far higher share than anywhere else in the nation.

The DeVoses, the most prominent name in state Republican politics, have been the biggest financial and political backers of the effort.

But if Michigan is a center of school choice, it is also among the worst places to argue that choice has made schools better. As the state embraced and then expanded charters over the past two decades, its rank has fallen on national reading and math tests. Most charter schools perform below the state average.

And a federal review in 2015 found “an unreasonably high” percentage of charter schools on the list of the state’s lowest-performing schools. The number of charter schools on that list had doubled since 2010, after the passage of a law a group financed by Ms. DeVos pushed to expand the schools. The group blocked a provision in that law that would have prevented failing schools from expanding or replicating.