Way back in 1944, FBI Director J. Edgar Hoover opened a file on teen idol Frank Sinatra for “corrupting the morals of America’s youth.”

Of course, “Frankie Swoonatra” became over time “The Chairman of the Board” and the voice of the Greatest Generation. So it’s hard to remember after all these years that at one time the fuddy-duddies were convinced Francis Albert and his acolytes were going to be the ruin of the nation.

Every generation is convinced the next generation is going to shove America off a cliff.

Boomers will long remember how the Greatest Generation were convinced the sacrifices they made on D-Day and the beaches of Anzio and Iwo Jima were evaporating in a cloud of pot smoke.

With their long hair and unisex clothes, you couldn’t tell the boys from the girls. Somehow boomers figured out what went where and America managed to survive.

Now it’s the boomers turn to point fingers at a new generation.

A study by Glendale-based Educational Testing Service suggests Millennials, the so-called Generation Y, made up of 16-34 year-olds, may in fact be the final nail in America’s coffin.

According to researchers at ETS, a nonprofit that has administered over 50 million tests in 180 countries, “Millennials are often portrayed as being on track to be our best educated generation ever, but their skill levels are comparatively weak,” says Madeline Goodman, one of the study’s authors.

Millennials in America ranked dead last compared to their contemporaries in 22 other countries.

“It doesn’t look like we’re in a good place with the future workforce, parents and citizens,” Goodman told the New York Daily News, putting the cherry on top of the cynicism sundae.

Generation Y also brought up the rear when it came to math and only Millennials in Spain and Italy ranked lower in reading and writing.

In the interest of full disclosure, I can’t count to 15 unless I kick off one shoe.

Still, it’s a little unnerving to think someday soon we have to turn over the keys to the world. If not Millennials, who? Japanese robots?

I was in New York last week, and every time I travel I’m struck by how remarkably complex the First World is. From the air traffic control system to rail lines and the power grid, this enormous country is crisscrossed with wires and pipes and towers and physical systems that require technical mastery to keep everything up and running.

I’m still waiting for Time Warner to fix our cable box.

But these kids today are great with computers, so what’s the problem?

Well, Educational Testing Service says, surprisingly, America’s Millennials also crash and burn when it comes to using computer applications to solve work-related problems.

Apparently all those hours playing “Grand Theft Auto” hasn’t produced a generation of digital geniuses. What happens when the last of our engineers and electricians, plumbers and planners are sent to the home for Jell-O at 5? Even the digital world will need welders.

A few months back I was wandering around the hardware store, a very analog activity in itself, when a nice young man, a new hire, offered to help retrieve an air conditioner filter from a top shelf.

At the register, his boss asked him to run out to the mailbox and mail a stack of letters. A few minutes later he returned, tail between his legs, and the stack of letters till in his hand.

“You don’t know what a mailbox is, do you?” asked the boss.

“No,” said America’s future.

And to be clear, this young man is not dumb, he had simply never mailed a letter in his life. The big blue metal box on the sidewalk was as mysterious to him as the Kardashians’ wealth and fame is to me.

Nobody’s born knowing anything.

Doug McIntyre’s column writes occasionally for the Daily News. He can be reached at: doug@kabc.com.