Betsy DeVos was picked to run the Education Department largely to continue the work she had embraced through her philanthropic work: advocating an expansion of charter schools. Hers was the most controversial Cabinet nomination by President Trump, requiring Vice President Pence to cast a tie-breaking vote confirming her for the position. That controversy had many causes, but a significant one was that many in the education community were concerned about turning over the department to someone who advocated transferring scarce public funding to what amounted to educational experiments.

Which is to say that DeVos should, by now, be very aware that her advocacy of charter schools is contentious, to understate it a bit. Meaning, by extension, that when being interviewed by one of the most established television news programs in the country, she should be able to defend her position.

Yet when interviewed by “60 Minutes” for a program that aired on Sunday — she wasn’t.

“In places where there is a lot of choice that’s been introduced,” DeVos told CBS’s Lesley Stahl, “Florida, for example, studies show that when there’s a large number of students that opt to go to a different school or different schools, the traditional public schools actually, the results get better as well.”

This is DeVos’s core case. Introducing charter schools forces public schools into the sort of competition you see in the free market, forcing the public institutions to improve. It’s a market-based proposal for solving the endemic problem of low-performing schools. Florida, DeVos argues, is an example of where it works.

But Stahl was prepared for this.

“Have the public schools in Michigan gotten better?” Stahl asked. Michigan is a key litmus test because it’s the place where DeVos’s pre-government advocacy was centered. DeVos stumbled over a response.

“Your argument that if you take funds away that the schools will get better is not working in Michigan,” Stahl said. “Where you had a huge impact and influence over the direction of the school system here.” She later added, “The public schools here are doing worse than they did.”

DeVos didn’t have much of a response except to point to “pockets” where schools had improved (without identifying any).

There are only two reasons that DeVos might not have been able to defend her position when confronted with the example of her home state. One is that she was simply unprepared for the interview and didn’t have a team in place that could have ensured she was ready for an inevitable line of inquisition from Stahl.

Education Secretary Betsy DeVos has been steeped in controversy since she was first nominated for the role in the Trump administration. (Claritza Jimenez/The Washington Post)

The other is that DeVos’s case isn’t as clear-cut as she presented it.

A 2009 study from the Rand Corp. found “little evidence that the presence of charter schools affects the achievement scores of students in nearby traditional public schools either positively or negatively.” A number of studies since have found similarly murky results.

We can look at this another way. Using data from the Education Department, the National Alliance for Public Charter Schools and the National Assessment of Educational Progress, we looked at charter school enrollment and educational achievement in nearly 30 states between 2005 and 2015.

The educational achievement data indicated the percentage of students in fourth or eighth grade who had attained basic proficiency in math and reading. We compared the change in those four percentages with the national change from 2005 to 2015. Then, we cross-referenced those changes with the increase in charter school student enrollment as a percentage of public school enrollment. (In other words, if there were 10 charter and 20 public school students in 2005 and 15 charter and 25 public in 2015, the percent change was from 50 percent to 60 percent — an increase of 10 percentage points.)

Overall, the correlation was small, meaning that you couldn’t predict an increase in achievement in math and reading proficiency based on the increase in charter school enrollment. The strongest link was in eighth-grade reading scores.

There was an outlier that DeVos should have championed, and it wasn’t Florida: Arizona saw a big increase in charter-school enrollment and big gains in proficiency in the state’s public schools. In three of the four grade-subject combinations, Florida did better than the nation overall. In all four, Michigan did worse.

Looking at the six states with the biggest shift to charter-school enrollment (picking six because it includes Michigan), results were mixed. In eighth-grade reading and math, four of the six states outperformed national gains between 2005 and 2015. In fourth-grade reading, half did. In fourth-grade math proficiency, only two of six did.

Our analysis above doesn’t pick out specific areas within states where charter schools may have been introduced, which might show a tighter correlation. A 2016 analysis of New York City schools found positive effects in public schools near charter programs, but that effect was linked to increased spending at those public schools, not necessarily increased competition.

DeVos claimed that giving students a choice of schools improved public schools. In states where more students took the choice to enroll in nonpublic schools, though, the results have been fairly scattershot. Meaning it was easy for Stahl and “60 Minutes” to introduce an example where DeVos’s rhetoric clearly doesn’t capture reality. That it was DeVos’s home state made it all the more possible that Stahl would ask DeVos to explain the discrepancy.

Yet, somehow, she wasn’t ready to do so.