PHILADELPHIA — Jordan Shapiro’s class delved into a weighty discussion of Plato’s allegory of the cave and shifting perceptions of reality.

Front and center on the classroom wall behind him flashed a constantly shifting series of posts on Twitter, all under the class hashtag of #Mosaic1.

With her Nook and phone at hand, sophomore Kaylyn Christian, 20, tweeted: “Are you really happy if you live a successful life in the shadows?”

Shapiro’s Temple University classroom is definitely not the norm in academia, but it could be a harbinger of the future.

While many professors ban tweeting and texting in class, Shapiro, a full-time instructor who started last year, encourages it. Even more so — he counts it as classroom participation. He often tweets back.

“Please tweet. Please do it,” Shapiro, 35, tells students at the start of the semester.

Christian, a psychology major from Princeton, is happy to comply.

“I always like to look up at the screen,” she said, “and see what others are saying, too.”

Dressed in a sleek black blazer and jeans with a woolly mop of hair, Shapiro looks and acts the part of the hipster instructor. He says on his Twitter page: “Doing my best to un-educate students at Temple University.”

He recently wrote a piece for Forbes — “Colleges Shouldn’t Be Jittery About Students Who Are Twittery” — outlining the conundrum playing out on campuses nationwide.

“The tech industry and university administrators are flooding institutions with online-learning platforms, filling classrooms with new smart tools, and trying to equip their students with the digital skills that appeal to corporate employers,” he wrote.

“Meanwhile, the faculty prefers to play the part of the curmudgeonly old guard — the ogre at the bridge, trying to keep innovation from crossing. Many professors ban all electronics from their classrooms. Others penalize students who are caught tweeting or texting by marking them absent for the day.”

Gets students excited

What really made Shapiro happy during class recently was Elizabeth Moore, 25, a junior advertising major from Penn Valley, who vigorously pounded on her phone as discussion ensued.

“I was actually on Facebook and also texting,” Moore said later. She was excited about the discussion and wanted to tell a poet friend who “is very into this whole reality thing” so she could share his quotes with the class on the Twitter feed.

“Socializing about Plato? Is there a better thing? That’s how they’re using their phones,” Shapiro said. “I felt completely validated.”

Shapiro emphasized that he was not critical of professors who do not use Twitter, such as his colleague Richard Libowitz, an associate professor who teaches the same humanities class. It’s a required general-education course designed to teach students to think critically and to express themselves articulately.

Libowitz, 64, bans tweeting, texting and other phone uses in class.

“I find tweeting kind of annoying,” said Libowitz, a self-described technological Luddite. “It’s worse than passing notes when we were kids.”

Technological expertise aside, Libowitz is disturbed that the written word has been overrun by a new language — that of the tweet.

“I’m still old-fashioned enough that I think the best way of learning is reading and talking,” he said.

There’s no wrong or right answer, said Sree Sreenivasan, chief digital officer at Columbia University. Each professor must decide which technology supports his or her teaching best.

If students are tweeting, he said, “there has to be a purpose.”

Temple has no formal policy on tweeting in class; it’s up to each professor, a spokeswoman said.

During a recent class, Libowitz used an older technology to help inform a discussion on the role marijuana plays in society. He showed film clips from “Reefer Madness” and “History of the World: Part 1,” and Michael Pollan’s “The Botany of Desire.”

His students followed the rules and kept their phones away — and none said they minded. “If my phone is out, I’m honestly not paying attention,” said Taylor Dugger, 19, a public-health major from Brooklyn, N.Y.