History lesson? Hardly.

That’s what many teachers who assigned American kids to watch the presidential debates as homework thought they were doing.

But presidential politics is your new sex-ed, kids. And Donald Trump is the sickening teacher.

Just wait until they start acting this stuff out.

We’ve been here before, of course, when Bill Clinton was in office and parents had to explain other ways people use cigars. Naturally, Trump couldn’t resist reminding us of all those scandals as he tried to deflect his own — a relentless and appalling loop of him bragging in 2005 about kissing, groping and hitting on women.

Parents nationwide scrambled to change channels and turn dials as the day’s news became nastier than uncensored Lil Wayne.

You think we reached a new low earlier this year, when white kids chanted “Build the wall” at Latino kids at a basketball game? Or when the Muslim kids at an elementary school were told they’d be deported soon? Or when the black kids on a hockey team got hit with the n-word over and over again during a game?

We can now add to that list the kindergartners and first-graders confused by reports of a presidential candidate describing grabbing kitty cats.

Welcome to The Trump Effect, in full blossom.

[The Trump Effect is contaminating our kids — and could resonate for years]

This is something I wrote about in early March, when the escalating hate talk of Trump’s presidential primary campaign began encouraging ugliness in schools and on playgrounds across the country.

Two weeks later, the Southern Poverty Law Center began a survey project to take the temperature of American classrooms.

Teachers who usually delve into election season for lesson plans told researchers that this year is different.

“It’s producing an alarming level of fear and anxiety among children of color and inflaming racial and ethnic tensions in the classroom. Many students worry about being deported,” Maureen B. Costello wrote in the center’s report on The Trump Effect.

“Other students have been emboldened by the divisive, often juvenile rhetoric in the campaign. Teachers have noted an increase in bullying, harassment and intimidation of students whose races, religions or nationalities have been the verbal targets of candidates on the campaign trail,” Costello said.

Just a few weeks ago, high school students in Montana showed up at a “Color Wars” pep rally wearing T-shirts declaring “White Pride” and “Trump 2016” inked on them. Nothing like that had ever happened at Polson High School before during Homecoming week, a school official said.

And now, we have graphic descriptions of sexual assault to wrangle with. You see the danger, right?

He urges “Build a wall,” and kids chant it at school.

He declares “Get ’em out,” and kids repeat it on the playground.

He says “Grab them by the p---y,” and, well, you know.

On Sunday night, Hillary Clinton talked about the whole phenomenon. “You know, children listen to what is being said,” she said. “And there’s a lot of fear — in fact, teachers and parents are calling it The Trump Effect.”

Trump supporters, of course, love that he says what’s on his mind. Funny, we used to call that rude. And it’s not just kids buying into his worst rhetoric.

He has ripped up our country’s social compact of modern decency. We’ve been slowly, painfully moving away from a bitter past, when people could be marginalized, fired, jailed or even killed because of the color of their skin, the object of their desire, the place of their birth, the coding in their DNA.

Decades of progress toward a more just and humane world have been lost in one heinous and dangerous year.

Adults are back to hearing the kind of insults their parents once endured.

In supposedly liberal Manhattan this past weekend, New York Times editor Michael Luo and his family encountered a “well dressed woman” on the Upper East Side so annoyed by their stroller that she yells, “Go back to China” and “Go back to your f---ing country.” Now Luo’s 7-year-old daughter keeps asking her parents, “Why did she say, ‘Go back to China?’ We’re not from China.”

In Maryland, a woman lounging by a pool in June insulted a U.S. military veteran and his wife as they were house-hunting with their Realtor, Fernando Herboso.

“We don’t want Muslims in our clubhouse,” she told them.

[A home that looks perfect until bigotry rears its ugly head]

Then Herboso, a lifelong Republican who said he has never faced bigotry since he immigrated to the United States almost 40 years ago, was attacked by his own colleagues over his heritage.

“I don’t even know what Hispanic means. Are you from Spain, Mexico, Argentina, Guatemala, Cuba? Does it really matter?” a co-worker told him. “I have to assume that it refers to some culture that you relate with that is different than the American culture. But what do you put first, Hispanic or American?”

Earlier this month, a kindergarten teacher’s aide in Georgia — you know, the kind who helps create the foundation for children’s behavior — was fired after she used Facebook to describe first lady Michelle Obama as a “gorilla.”

And then there’s Andrew Weinstein, who used to be an aide to former House speaker Newt Gingrich (R-Ga.) before he began organizing Washington Republicans against Trump. He had to go to the FBI because of anti-Semitic death threats. They included cartoons of Jews being forced into ovens. I get tagged on a lot of them because I wrote about him once.

Patrice Brock, one of the undecided voters chosen to ask the candidates questions, began Sunday night’s town-hall debate with this one:

“Knowing that educators assign viewing the presidential debates as students’ homework, do you feel you’re modeling appropriate and positive behavior for today’s youth?”

Pushed by co-moderator Anderson Cooper to acknowledge that he was bragging about sexual assault on the “Access Hollywood” videotape, Trump refused to do so.

“No, I didn’t say that at all,” he replied. “I don’t think you understood what was — this was locker room talk.”

Denise Rucker Krepp, a neighbor of mine in D.C., said her daughter was supposed to watch the second presidential debate for her history class.

“I just told her to go to bed,” Krepp said. “I’m not going to subject her to Donald Trump and his locker room behavior.”

But it’s too late for the rest of us to escape what we’ve seen and heard over the past year. Not even a good night’s sleep or a Trump defeat on Nov. 8 could reverse the divisiveness and meanness that Trump has unleashed on our country.

Twitter: @petulad