They just weren’t in on the joke. And in a way, they were left out of the national discussion — but trying, in fits and starts, to jump in wherever they could.

The texts also contained essays with jargon such as “postmodern” and “images of women in the media,” which assumed not only knowledge of the culture, but a knowing ironic attitude toward it. I found myself explaining (encyclopedically) and portraying (like a bad sketch comedian) America in the ’80s and ’90s just to begin a discussion of an article.

This failure to get the joke, this lack of a common vocabulary — especially the vocabulary of our supposedly shared American culture — is more than a barrier to teaching. It’s also a barrier to widespread acknowledgment of the ways in which foreigners enrich our lives.

Sometimes, to give the class a break, I’d tell a joke, one carefully chosen for its narrative simplicity and limited vocabulary. But this, too, was stepping into the same minefield.

I used to try a guy-walks-into-a-bar-with-a-dog story, one known by most 10-year-old Americans. It involves the terms “roof,” “Ruth,” “woof” and “Barry Bonds,” and I perform it with what I regard as Jim Carrey-level skill.

Well, the sheer tonnage of cultural information in the joke was staggering. “American baseball?” I would say. “It’s like cricket, you know? Oh, cricket? It’s a game played in former British colonies.” The 10 minutes of grinding, numbing explanation left me exhausted and left the students wondering if it was too late to transfer to a saner class.

So I shifted again, and now I have them write what I consider doable essays, ones that discuss lifestyle and family issues that appear in magazines and newspapers. Reacting to these articles gives them the opportunity to tell their stories. Of course, I still hit the pop-culture reference problem, but the essay results have been riveting.

By talking about their own lives, they tell stories that are absorbing, powerful and unexpected, such as the story of Nang Ying from Myanmar, who escaped a forced labor camp in her teens; and Mohammed from Mogadishu, who as a boy witnessed countless killings in the streets; and Neil, who went AWOL from Saddam Hussein’s army in Iraq. All of them love America with a passion most native-born citizens would find hard to fathom.

These writers haven’t met my students or read their stories. And they haven’t opened their eyes to the blessings immigrants bring.

Several weeks ago, my wife and I found ourselves in a hospital emergency room with our disabled son. One of the nurses, warm, caring and coolly professional, was especially reassuring. After our boy was on his feet again and we were breathing normally, the nurse said, “Dr. Hughes, do you recognize me? I was your student five years ago.” I stared at her for a moment, embarrassed, and then suddenly remembered: Baredu Bedaso from Ethiopia. Not a strong writer, seldom got the joke, clueless about American pop culture.

But none of that mattered. She had found a role in America that positioned her to save lives.

Could she now identify Homer Simpson? I forgot to ask.