Ordinarily, a professor would worry if only one out of every 10 students passed a class. But University of Virginia historian Philip Zelikow seems enormously pleased with such results from the course he just finished teaching on the history of the modern world.

About 10 percent passed his class. That works out to nearly 5,000 of roughly 47,000 who registered.

Much is made of the gargantuan number of students who sign up for massive open online courses, or MOOCs. After all, that is why they are called massive.

Coursera, the Web platform that hosted Zelikow’s MOOC and many others, has drawn more than 3.5 million registered users. EdX, another MOOC platform, has more than 890,000.

But the metrics for Zelikow’s MOOC on global history since 1760 — which The Post in late February featured in a an article on lecture methods and a first-person account on taking a MOOC — suggest that registration numbers are not what matters most.

“A large fraction of course registrants never even glance at the course they enrolled in,” Zelikow wrote in an e-mail. This seems to be true for many MOOCs, and perhaps most.

These registrants, who can sign up for a class with a mouse click and pay nothing to do so, aren’t necessarily students at all. They are simply browsing, like people who stroll through the aisles of a bookstore and make notes to themselves about something they want to read soon — but never do.

Analyzing data on how many of his 92 video lectures were viewed and how many weekly quizzes were taken, Zelikow calculates that about 26,000 sampled the course at least briefly and that about 13,000 to 15,000 “decided to give it a go.”

Of that group, he said, nearly 5,000 earned statements of accomplishment by obtaining a minimum score on the weekly multiple-choice quizzes.

Using the “sample” crowd for comparison, the pass rate for the MOOC was nearly one out of five. Using the “give it a go” crowd, it was maybe one in three.

By the way, those statements can be printed out. (I earned one myself and just did so.) What are they worth? Who knows? There’s a footnote that makes clear that the statements convey no credits from U-Va.

Zelikow said he believes maybe an additional 5,000 people audited the course “pretty thoroughly without bothering with the exams. In addition, there were 946,000 unique views of his lectures.

“[W]hat stands out is that this course has helped a great many people think about our common history and that this has enriched their lives,” Zelikow wrote this week in a final message addressed to “fellow learners.” He added that he had never had a more satisfying experience in his career as a teacher.

“One point I stress is that my university, and others, [are] now reaching a very large number of non-traditional students, who are at least as eager to learn as many of those we see in our classrooms,” Zelikow wrote. “Institutions of higher education will need to think hard about how we can serve — and learn from — more students like you.”

A course survey that drew more than 5,000 responses found that more than 40 percent who took the MOOC were 45 or older. Most held at least a bachelor’s degree, were not alumni of U-Va. and didn’t know anything about the professor. (Zelikow serves on President Obama’s Intelligence Advisory Board and was executive director of the 9/11 Commission during the presidency of George W. Bush.)

Basically, a large number who took the MOOC were lifelong learners.

As a student named Tania Vardi wrote on a course discussion board: “I’m 68 years old, no university degree but History always being my favorite subject I enjoyed very much this ‘ride’ through the modern world history as you present it to us. It’s been a privilege having such a teacher. The wonders of internet!!!!”

The MOOC also was required for U-Va. students who took a live, parallel version of the class on campus with Zelikow. They were part of an experiment in “flipping” the classroom — watching lectures online on their own time, then coming to class for seminar-style discussions. Initial surveys suggested that many of those students liked the MOOC too. But some found that taking the online version and the U-Va. class simultaneously produced a “much heavier workload for them than they were accustomed to in their other courses,” according to Zelikow.