Jeb Bush had this big idea about how to hold schools accountable: Give them a letter grade based mostly on their test scores. The schools with high grades can bask in their success, and the schools with low grades will get a warning, maybe some extra help, but if they fail to get higher grades, they can be closed and turned over to charter operators. Nice way to combine testing and privatization.

But, it turns out that the test scores mostly measure family income, so the letter grades measure family income. Instead of showing whether a school is high quality or low quality, the grades simply reflect the wealth or poverty of the community. But you knew that without giving a test.

Mercedes Schneider observes the same phenomenon in the latest letter grades in Louisiana. Then she looks around and finds that every state that uses letter grading of schools is getting the same results.

If you already know the income level of the community, you could just skip the tests and hand out the grades. Rich neighborhoods get an A, and poor neighborhoods get an F.