One of the dirty secrets about MOOCs — massive open online courses — is that they are not very effective, at least if you measure effectiveness in terms of completion rates.

If as few as 20 percent of students finishing an online course is considered a wild success and 10 percent and lower is standard, then it would appear that MOOCs are still more of a hobby than a viable alternative to traditional classroom education.

Backers reason that the law of large numbers argues in favor of the online courses that have rapidly come to be seen as the vehicle for the Internet’s next big disruption — colleges. If 100,000 students take a free online course and only 5,000 complete it, that is still a significant number.

However, MOOCs are a moving target. Because they are computerized and networked they offer an ideal medium for quantifying what works and what doesn’t. Earlier this week, when San Jose State University in California announced that it was contracting with MOOC-developer Udacity to create three pilot classes, they noted that the National Science Foundation had agreed to fund research to study the impact of the classes.

Udacity, along with other MOOC designers, is moving rapidly away from the video lecture model of teaching toward an approach that is highly interactive and based on frequent quizzes and human “mentors” to provide active online support for students.

Moreover, there are early indications that the high interactivity and personalized feedback of online education might ultimately offer a learning structure that can’t be matched by the traditional classroom.

Duolingo, a free Web-based language learning system that grew out of a Carnegie Mellon University research project, is not an example of a traditional MOOC. However, the system, which now teaches German, French, Portuguese, Italian, Spanish and English, has roughly one million users and about 100,000 people spend time on the site daily. The firm’s business is based on the possibility of using students to translate documents in a crowd-sourced fashion.

Seventy-five percent of the students are outside of United States, and Carnegie Mellon computer scientist Luis von Ahn notes that the foreign students are significantly more motivated and have a higher completion rate than their American counterparts.

The firm, which was founded by Dr. von Ahn and his students, commissioned a study of the effectiveness of the language training system that indicates that students may learn languages more quickly online. Conducted this fall by Roumen Vesselinov, a visiting assistant professor of economics at Queens College, City University of New York, and John Grego, chairman of the statistics department at the University of South Carolina, the study compared Duolingo to offline learners and found that on average a person with no knowledge of Spanish would need an average of 34 hours to cover the material for the equivalent of a first college semester. Although, the number of class hours for a college language class vary for a semester, Dr. von Ahn said that a course at Carnegie Mellon might require roughly 135 hours of course time.

The researchers reported: “The main factor for higher effectiveness was the motivation of the participants with people studying for travel gaining the most and people studying for personal interest gaining the least. Another factor for higher effectiveness was the initial level of knowledge of Spanish with beginners gaining the most and more advanced learners gaining the least.”

The researchers have previously conducted studies of the effectiveness of other commercial learning programs such as Rosetta Stone, Auralog and Berlitz, and in this case they began with a sample of 556 students who were using the Duolingo service.

Dr. von Ahn acknowledged that the results are preliminary, and the researchers noted that it was not possible to generalize beyond the study of Spanish based on their sample. However, he noted that with other researchers he has started a longer, more general study. In the meantime, Duolingo has continued to grow at a MOOC pace — the service is picking up between 15,000 and 20,000 new users daily and Dr. von Ahn said that it might expand by as much as five times in the coming year.

The company is now working to add Chinese to its list of languages, with a particular focus on teaching English to Chinese speakers. “It turns out that there are 1.2 billion people in the world who want to learn a foreign language, and 400 million of them are in China,” he said.