The argument over tenure for university professors is a long and boisterous one.
Levitt, for one, is in favor of abolition. If you are on that side of the argument as well, you may be pleased to read a new working paper by David Figlio, Morton Schapiro, and Kevin Soter (all associated with Northwestern, in one capacity or another) called "Are Tenure Track Professors Better Teachers?" (gated, sorry). Short answer (in their study, at least): no.
This study makes use of detailed student-level data from eight cohorts of first-year students at Northwestern University to investigate the relative effects of tenure track/tenured versus non-tenure line faculty on student learning. We focus on classes taken during a student’s first term at Northwestern, and employ a unique identification strategy in which we control for both student-level fixed effects and next-class-taken fixed effects to measure the degree to which non-tenure line faculty contribute more or less to lasting student learning than do other faculty. We find consistent evidence that students learn relatively more from non-tenure line professors in their introductory courses. These differences are present across a wide variety of subject areas, and are particularly pronounced for Northwestern’s average students and less-qualified students.