** Also posted here on “Valerie Strauss’ Answer Sheet” in the Washington Post
Over the weekend, New York Times columnist Nick Kristof made a persuasive argument that teachers should be paid more. In making his case, he also put forth a point that you’ve probably heard before: “One Los Angeles study found that having a teacher from the 25 percent most effective group of teachers for four years in a row would be enough to eliminate the black-white achievement gap."
This is an instance of what we might call the "X consecutive teachers” argument (sometimes it’s three, sometimes four or five). It is often invoked to support, directly or indirectly, specific policy prescriptions, such as merit pay, ending tenure, or, in this case, higher salaries (see also here and here). To his credit, Kristof’s use of the argument is on the cautious side, but there are plenty of examples in which it used as evidence supporting particular policies.
Actually, the day after the column ran, in a 60 Minutes segment featuring “The Equity Project," a charter school that pays its teachers $125,000 a year, the school’s principal was asked how he planned to narrow the achievement gap with his school. His reply was: “The difference between a great teacher and a mediocre or poor teacher is several grade levels of achievement in a given year. A school that focuses all of its energy and its resources on fantastic teaching can bridge the achievement gap."
Indeed, it is among the most common arguments in our education policy debate today. In reality, however, it is little more than a stylistic riff on empirical research findings, and a rough one at that. It is not at all useful when it comes to choosing between different policy options.