A recent study of tenured faculty has found that, on average, professors receive worse student evaluations after receiving tenure, a senior status that grants job security to experienced academics.

This study reinforces mounting concerns over the role tenure plays in higher education, as critics say that it protects bad professors and that the enhanced job security allows tenured faculty to neglect their teaching obligations.

Researchers from the University of New Haven and California State University, Chico, conducted the study, and they focused on a sample of 250 tenured professors from the University of Colorado Boulder. Each professor in the sample received tenure over an 11-year period ending in 2017. To be fair, this sample may not be representative of tenured professors at every university across the country. But the results at UC Boulder were clear.

Post-tenure faculty saw a “small, but persistent, decline” in student evaluations. This effect was most significant during the semester right after a professor receives tenure.

This makes sense, as it’s clear that any employee’s incentive to perform at a high level would drop if they knew they had their job security all but guaranteed. At the very least, tenure drastically changes the incentive structure of a professor’s day-to-day tasks, making instructors more likely to prioritize research or other projects over teaching. This is in clear opposition to the mission of most universities, which are supposed to be focused on educating students.

Some at UC Boulder are seeking to cover up the trend revealed by this study. Faculty there backed a resolution last year that said evaluative questions about overall performance should be removed, because they supposedly open up opportunities for students to subject faculty who belong to “protected classes” to bias. However, this alleged bias against certain professors cannot explain the study’s findings. It is highly unlikely that students taking a class with a professor who has recently received tenure are disproportionately more biased than the professor’s previous students.

The American Association of University Professors says that the “principal purpose” of tenure is ensuring academic freedom to research and speak on controversial topics. Academic freedom is certainly important, but taxpayers should not be paying salaries for government employees who can barely perform their primary function: educating students.

The tenure system needs reform — students paying thousands upon thousands for their education should not be forced to learn under disinterested professors.

Alexander James is a contributor to Red Alert Politics and a freelance journalist.