The government measures graduation rates as the percentage of first-time undergraduates who obtain a degree within six years. On average across all American universities, the rate is 55 percent. Dr. Pepicello said this was a poor yardstick for comparing other universities with his, which serves mostly older students who started college elsewhere. Alongside the 16 percent rate, the university Web site also publishes a 59 percent graduation rate, but that is based on nonstandard calculations and does not allow comparison with other universities, he said. The official rates at some University of Phoenix campuses are extremely low — 6 percent at the Southern California campus, 4 percent among online students — and he acknowledged extraordinary attrition among younger students.

Image Robert Wancha, who is pursuing a bachelors degree at the University of Phoenix, has criticized its standards. Credit... Fabrizio Costantini for The New York Times

“We have not done as good a job as we could,” he said, adding that the university was creating tutoring and other services to help keep students.

“The university takes quality in the classroom seriously,” he said. The university brings a low-overhead approach not only to its campuses, most of which are office buildings near freeways, but also to its academic model. About 95 percent of instructors are part-time, according to federal statistics, compared with an average of 47 percent across all universities. Most have full-time day jobs. Courses are written at university headquarters, easing class preparation time for instructors.

The College Board reports the university’s annual tuition and fees as $9,630, about half the average at private four-year colleges and twice that of four-year public colleges.

Students take one course at a time, online or in evening classes, which meet for four hours, once a week, for five or six weeks, depending on degree level. As a result, students spend 20 to 24 hours with an instructor during each course, compared with about 40 hours at a traditional university. The university also requires students to teach one another by working on projects for four or five hours per week in what it calls “learning teams.”

Government auditors in 2000 ruled that this schedule fell short of the minimum time required for federal aid programs, and the university paid a $6 million settlement. But in 2002, the Department of Education relaxed its requirements, and the university’s stripped-down schedule is an attractive feature for many adults eager to obtain a university degree while working. But critics say it leaves courses with little meat.