A cadre of critics — from conservative broadcaster Glenn Beck to Diane Ravitch, a newly prominent defender of traditional public education — are sounding the alarm about the Common Core, a new set of standards that will lead to national standardized English and math tests for K-12 schools. But the avalanche of antipathy at best misunderstands what the Common Core does. A common nationwide test, which is the real goal pushed by the Obama administration and codified by the Common Core State Standards Initiative, will not radically change our schools — but will make it easier to evaluate future curricular innovations. A common nationwide curriculum, meanwhile, is a terrifying but phantom bogeyman. No one is seriously proposing it. Yet the idea is being used to discredit the common tests that would enable us to better evaluate the approaches that different school districts choose. I serve on the advisory board of the Gates Foundation’s domestic program, a well-known supporter of the Common Core, and have yet to hear anyone suggest that the U.S. Department of Education should dictate what is taught in every American classroom. In exchange for $250 million in funding from the federal Race to the Top initiative, Massachusetts did accept the federal objective of “developing and adopting common standards” — but that’s a matter of testing, not curriculum. The movement against the Common Core is partially fueled by a suspicion of federal intrusion into traditionally local functions. But some federal interventions are helpful. The increases in math and science education that followed the famous Reagan-era “A Nation at Risk” report significantly increased earnings for African-American males. Moreover, leaving local districts entirely to their own devices hasn’t worked. The first Trends in International Mathematics and Science Study in 1999 found that our eighth graders did worse than their peers in 18 out of 37 countries. The federal government was right to start nudging local school districts with programs like No Child Left Behind. Reform requires measurement. How can we know where to invest, if we can’t measure failure or success? But the price of passing No Child Left Behind was that states were left free to design their own evaluation systems, so it has been far easier to get by in some states than others. At the heart of the Common Core is the desire for a standardized yardstick. The Common Core has attracted a variety of criticisms. Some commentators have complained about the costs of implementation, measured both in cash and in the time students spend taking tests. Glenn Beck believes that the Common Core “will invite greater and greater indoctrination and bias.” Jim Stergios of the Pioneer Institute sensibly worries that the test will lower Massachusetts’ already high standards, and that children will get less great literature and no algebra until high school. Diane Ravitch is troubled about the lack of a “field test” showing the efficacy of the Common Core. None of these concerns should worry us, as long as the Common Core is limited to a common national test. In fact, test taking is an invaluable part of the learning process, and the costs of implementing it, estimated by Pioneer at $15.8 billion, are small relative to the overall cost of education or the benefits of improving our schools. There is no requirement to slip in leftist indoctrination or cut great books; indeed, the English standards mention Shakespeare, Ovid and the Bible. Curricula will still be decided locally, so it’s great that Stergios is fighting for “Huckleberry Finn.” As for Ravitch, her passion for field tests is admirable; but assessing curricular experiments demands a standardized measure — and that’s what the Common Core provides. People who fear a standardized national curriculum, as I do, rightly worry about whether testing will distort course instruction. These fears are not baseless: The state has offered detailed curriculum frameworks targeted towards Common Core tests. But these frameworks are voluntary, and school districts and teachers can readily choose to include more or different material, if they think it will produce better results. In the meantime, the best way for Massachusetts to prevent a dumbing-down of instruction is to press constantly for higher standards — and perhaps even to have a state-specific test that goes beyond the Common Core. Performance on a common test will help evaluate which curricula are most effective, which is why the Common Core test will do the most good when individual states and districts experiment widely. Edward L. Glaeser, a Harvard economist, is director of the Rappaport Institute for Greater Boston.