Betsy DeVos’s favorite education policy keeps looking worse. Last week, the Education Department, which she runs, released a careful study of the District of Columbia’s use of school vouchers, which she supports. The results were not good.

Students using vouchers to attend a private school did worse on math and reading than similar students in public school, the study found. It comes after other studies, in Ohio and elsewhere, have also shown weak results for vouchers.

To channel President Trump: Who knew that education could be so complicated?

The question for DeVos is whether she’s an ideologue committed to prior beliefs regardless of facts or someone who has an open mind. But that question doesn’t apply only to DeVos. It also applies to all of us trying to think about education, including her critics. And the results from Washington are important partly because they defy easy ideological conclusions.

Before diving into those results, I want to make two broader points. First, education isn’t just another issue. It is the most powerful force for accelerating economic growth, reducing poverty and lifting middle-class living standards. Well-educated adults earn much more, live longer and are happier than poorly educated adults. When researchers try to tease out whether education does much to cause these benefits, the answer appears to be yes.