A little-noticed but unusually detailed study of teaching practices, reported by Robert Rothman in the November/December issue of the Harvard Education Letter, delivers a depressing message you should keep in mind whenever you read anything about raising school achievement. I don’t care if it’s by an education school dean, or a state governor, or the U.S. secretary of education, or even me. If this new study is true then none of us really knows what we are talking about.