A major new study has found that new students at Northwestern University learn more when their instructors are adjuncts than when they are tenure-track professors.

The study -- released this morning by the National Bureau of Economic Research (abstract available here) -- found that the gains are greatest for the students with the weakest academic preparation. And the study found that the gains extended across a wide range of disciplines. The authors of the study suggest that by looking at measures of student learning, and not just course or program completion, their work may provide a significant advance in understanding the impact of non-tenure-track instructors.

Many adjuncts will no doubt be pleased by the study's conclusions on their teaching ability. But the study does not call for an end to the two-tiered system of academic employment between those on and off the tenure track. Rather, it says that the study may provide evidence that research universities benefit from more teaching by those who don't have research obligations.

"There are many aspects relating to changes in the tenure status of faculty – from the impact on research productivity to the protection of academic freedom," the study says. "But certainly learning outcomes are an important consideration in evaluating whether the observed trend away from tenure track/tenured towards non-tenure line faculty is good or bad. Our results provide evidence that the rise of full-time designated teachers at U.S. colleges and universities may be less of a cause for alarm than some people think, and indeed, may actually be educationally beneficial. Perhaps 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 multi-tasking problem," says the paper.

The authors of the study are David Figlio, the Orrington Lunt Professor of Education and Social Policy and of Economics at Northwestern; Morton O. Schapiro, Northwestern's president (and a long-time scholar of higher education economics); and Kevin B. Soter, a management consultant.

In their new paper, they note that previous studies have looked at the impact of adjunct instructors on graduation rates and retention rates. But they argue that it is important to shift the analysis to student learning and to behavior associated with student learning. Northwestern's first-year students turn out to be good research subjects because most of them take at least one course from a non-tenure-track instructor and at least one from a tenure-track or tenured professor.

The study tracked eight cohorts of freshmen (those who entered from fall 2001 through fall 2008), and looked not at the grades or completion in the courses taught by the adjuncts, but at whether students enrolled in another course in that subject and the grades that students earned in that course. The study found that students were significantly more likely to enroll in a second course in the subject when the first course had been taught by an adjunct, and that they were likely to earn a higher grade in that second course if the first had been taught by an adjunct.

"Moreover, the results held for all subjects, regardless of grading standards or the qualifications of the students the subjects attracted, though we found that the results were particularly strong for tougher-grading subjects and those that attracted the most qualified students," the authors write. "In addition, we found that the apparent benefits of taking classes from non-tenure track faculty were enjoyed more by the less academically qualified students than by the more academically qualified students -- the biggest gains to faculty outside the tenure system were for relatively weak students taking courses in the toughest-grading subjects."

The authors acknowledge that Northwestern is not a typical college. It has highly competitive admissions and more resources to hire faculty members (tenure-track or not) than is the case for many other colleges. However, they add that "our findings that the benefits of taking courses with non-tenure track faculty appear to be stronger for the relatively marginal students at Northwestern indicate that our findings may be relevant to a considerably wider range of institutions."