Students learned more when their first instructor in a discipline was not on the tenure track, as compared with those whose introductory professor was tenured, according to a new paper from Northwestern University.
The paper, "Are Tenure-Track Professors Better Teachers?," was released on Monday by the National Bureau of Economic Research, and it sheds new light on the hotly debated topic of whether the increased use of adjunct instructors is helping or hindering students' learning.
The researchers found "strong and consistent evidence that Northwestern faculty outside of the tenure system outperform tenure track/tenured professors in introductory undergraduate classrooms," wrote David N. Figlio, director of Northwestern's Institute for Policy Research; Morton O. Schapiro, the university's president; and Kevin B. Soter, an associate consultant at an organization called the Greatest Good, which uses economic methods and data analysis to help businesses.
They also found that students who were relatively less qualified academically fared particularly well when they were taught by faculty members outside the tenure system, especially in courses where high grades were generally tougher to earn.
"We tried every possible thing we could to see if this result was fragile," Mr. Figlio said in an interview. "In every single specification we tried, this result came up."
Mr. Figlio and his fellow researchers based their findings on a study of the academic performance of the eight cohorts of freshmen, totaling 15,662 students, who entered Northwestern from the fall of 2001 to the fall of 2008.
They analyzed students who in their first term took, say, an introductory economics course taught by an untenured instructor and an introductory political-science course led by a professor who was tenured or on the tenure track. Then the researchers studied what courses the students took during their second term: Did they take economics or political science? And how well did they do?
The students were more likely to take a second course in a discipline if the first had been taught by an untenured faculty member, and they were more likely to earn a better grade in the next course compared with students whose first course in the discipline had been taught by a tenured or tenure-track professor.
"A nontenure-track faculty member increases the likelihood that a student will take another class in the subject by 7.3 percentage points," the authors wrote, "and increases the grade earned in that subsequent class by slightly more than one-tenth of a grade point."
Northwestern uses a four-point scale for grade-point averages, which Mr. Figlio said is a better proxy for learning than student-satisfaction surveys or standardized tests. "It's not perfect," he said, "but frankly it's the only thing I can think of."
The fact that the study was conducted only on students at Northwestern makes it both useful and limited for its broader applicability.
Northwestern's students come from "a rarefied portion of the preparation distribution," the authors wrote, and are "far from reflective of the general student population."
In fact, students who were described in the study as less-qualified academically, according to the five-category system used by Northwestern's admissions office, still posted an average SAT score of 1316.
Indeed, a similar study of students conducted at a less-selective institution yielded less-striking results than Northwestern's. Matthew M. Chingos, of the Brookings Institution, analyzed 281 sections of algebra taught by 76 unique instructors at Glendale Community College, in California. Students whose sections had been taught by full-time instructors were about four percentage points more likely to earn a C or better on a common final examination than were those whose teachers had been part-timers, instructors whose working conditions more closely mirror those of untenured faculty members elsewhere.
But an untenured faculty member at Northwestern may not look much like the stereotype of a part-time instructor cobbling together teaching gigs on multiple campuses. Northwestern's were generally well compensated and enjoyed longstanding relationships with the university, said Mr. Figlio.
He added that 99.4 percent of the untenured faculty members in the study had taught at Northwestern for at least six quarters.
"This is not someone we're hiring once to fill a gap and then getting rid of," he said.
Northwestern's part-time faculty members earn from $4,200 to $7,334 per course, according to eight respondents to The Chronicle's Adjunct Project, a Web site that crowdsources salary data for contingent faculty members.
Administrators of colleges where adjuncts do not enjoy similar treatment "should not say this proves we should reduce the tenure system," said Mr. Figlio.
Instead, he and his fellow authors wrote, the results offer evidence that designating full-time faculty members to focus chiefly on teaching, particularly at research-intensive universities like Northwestern, may not be the cause for alarm that many see. It may even improve students' learning.
"Perhaps," they wrote, "the growing practice of hiring a combination of research-intensive tenure-track faculty members and teaching-intensive lecturers may be an efficient and educationally positive solution to a research university's multitasking problem."