Educators cite a variety of reasons – from aggressive student-retention programs to the decline in teenage pregnancies – but the sluggish economy appears to be the biggest reason our public school graduation rate is the highest in more than 30 years.

The Department of Education says 3.1 million high-school seniors earned a diploma in the spring of 2010, with 78 percent finishing on time, topping the previous best graduation rate of 75 percent in 1975-76.

From 2009 to 2010, the unemployment rate flirted with 10 percent, even higher for teenagers, and there were virtually no jobs for workers with no skills and little education.

“If you drop out of high school, how many good jobs are there out there for you? None. That wasn’t true 10 or 15 years ago,” Education Secretary Arne Duncan told the Associated Press.

Studies have shown that the earnings difference between a high school degree and no degree over a lifetime is $130,000.

At one time in America’s industrialized past, a high school dropout could readily find unskilled work on an assembly line, a steel mill, the oil fields or the mines and be paid enough to support a decent lifestyle. Those jobs are mostly gone, and there’s no prospect of their coming back. There are still manufacturing jobs out there – indeed, some of them are going begging – but they demand high levels of computer, math and technical skills.

The graduation figures don’t include those youngsters who took an extra year to complete their course work.

The national dropout rate, another perennial problem, fell to 3 percent after holding at 4 percent for the previous seven years.

The graduation and dropout rates vary widely by geography, race and ethnicity, according to the department.

White, Asian and Pacific Islanders’ most recent dropout rate was 2 percent; Hispanics, 5 percent; blacks, 6 percent; and American Indians and Alaskan natives, 7 percent.

Big cities tend to have higher dropout rates, with Washington, D.C., one of the worst at 7 percent. Arizona, at 8 percent, had the nation’s highest rate among states, followed by Mississippi at 7 percent.

These latest education figures replace a welter of not-always-reliable records from states, which routinely self-reported graduation rates of 80 percent to 90 percent or better.

Now we truly know where the problems are.