On the last day of 2015 the longest serving member of President Obama’s Cabinet, Arne Duncan, quietly stepped down from his official position as what the Washington Post called “the most powerful education secretary in U.S. history.” The federal government now provides about 10 percent of the money spent on public schools, and Duncan used that money, to an extent never before, to impose his will on local schools.

Arne’s departure is a good time to review what’s wrong with America’s public schools and how the federal government has made them worse. Instead of giving an account of his stewardship, however, Arne Duncan chose to devote his final speech to complaining about Congress’s failure to pass new gun-control laws.

Duncan’s gun-control speech was given in Chicago which, despite the nation’s most restrictive gun laws, nevertheless closed out the year 2015 with more homicides (at least 468) and shootings (over 2,900) than any other American city including New York and Los Angeles. With his call to deprive law-abiding citizens of the means of protecting themselves in their own homes, it’s no wonder that Arne Duncan was rated the most “anti-gun” member of Obama’s Cabinet by the National Rifle Association.

Duncan likes to brag that the high-school graduation rate edged upward to 82 percent during his tenure, but what he doesn’t say is that student achievement has simultaneously declined according to “the nation’s report card,” the National Assessment of Educational Progress. The NAEP test confirms that most of today’s high-school graduates simply haven’t learned what Americans expect high-school students to know, nor have they acquired the basic skills they need to support themselves and their future families.

The value of a high-school diploma, as measured by the earning power of high-school graduates, continues to decline, and the free-trade economy is creating fewer jobs that require no more than a high-school education. Students who graduate from high school today are much worse off economically than high-school graduates of one, two, or three generations ago.

The mantra of “college and career ready” is often used as the measure of what a high-school diploma is supposed to represent. Let’s take math, and especially algebra, mastery of which is necessary for any kind of STEM (science, technology, engineering, and math) career.

New York State uses the statewide Regents exam for high-school algebra in which a raw score of 30 out of 86 was “scaled” to a passing score of 65 (even though, if you do the math, 30 divided by 86 means that only 35 percent of the questions were answered correctly, not 65 percent). But only 63 percent of high-school seniors managed to achieve that so-called passing score, even after several tries; less than a quarter of the students attained the higher “college ready” score.

Even the term “college ready” is misleading, because it only means ready for a two-year community college with open admissions, not a competitive four-year college. At most community colleges, half the students must take “remediation” courses before they can even begin to do college-level work, and most students who enter remediation never earn a college degree.

The decline of public education explains the rebellion against the Common Core, which was foisted on the nation without public approval. It explains why in the Republican presidential contest, all the governors (Bush, Walker, Kasich, Christie, and Huckabee) remain in single digits while the leading candidates say that Common Core is a disaster and pledge to do away with it.

Common Core produced voluminous standards for reading and math, replacing fiction and literature with instructional texts, and replacing computational shortcuts with useless busy-work. Its minimum standards were set low enough for nearly every student to pass, as if we’re in Lake Wobegon, where “all the children are above average.”

Speaking on December 22 at the high-school gym in Keota, Iowa, Hillary Clinton vowed, “I wouldn’t keep any school open that wasn’t doing a better than average job.” Math wasn’t my strongest subject, so I asked my granddaughter, who graduated from college with a math degree and now works as an actuary, to explain how Hillary’s proposal would work.

If Hillary really means to close any school “that wasn’t doing a better than average job,” that would mean closing half the nation’s 90,000 public schools next year, half the remaining schools the following year, and so on until just one school was left open. And then that one school would have to close too, because if there’s only one school, it can’t be “better than average.”

Of course Hillary, whose presidential campaign has already been endorsed by both teachers unions (the NEA and the AFT), doesn’t really intend to close all public schools. She just wants to continue pretending that every public school is “better than average” so that parents will have no choice about what their children are taught (or not taught).