Randi Weingarten, head of the American Federation of Teachers, makes the case for the national imposition of “common, rigorous standards” in education. I have read many such op-eds over the years, and in each case it is the “rigorous” rather than the “common” that generates the attractiveness of the proposals. Also in each case it is left unclear why we should expect federal standards to resemble the best state standards rather than the worst ones.