From an article featured in Washington Monthly:

The problem is that education master’s programs generally don’t produce better teachers. While programs vary greatly, and some stand above the rest, the teachers I interviewed told me that they had spent too much time on theory and not enough on practical teaching skills; professors were too far removed from the classroom and using out-of-date pedagogy; and many programs simply weren’t rigorous. Decades of research back up their critiques.

“When you talk to someone who is not in the weeds of ed research, they would be shocked that more education wouldn’t make a teacher more productive,” said Dan Goldhaber, who directs the Center for Education Data and Research at the University of Washington. But that’s what the data shows. Students whose teachers have a master’s degree don’t perform better on standardized tests—an incomplete but meaningful metric—than students whose teachers have just a bachelor’s degree.

Don’t believe Dr. Goldhaber?

“Most of the research is that there’s either no statistically significant difference, or small significant differences, in teachers with master’s degrees,” said Thomas Kane, an economist and professor of education at Harvard. Matthew Chingos, an education-policy expert at the Urban Institute, has described it as “one of the most consistent findings in education research.” Kate Walsh, president of the National Council on Teacher Quality, put it more bluntly: “It’s as conclusive as research that finds smoking causes lung cancer. It’s as conclusive as the research on climate change.”

Don’t believe Goldhaber, Kane, Chingos, or Walsh?

Marguerite Roza, an education-finance expert, got an inkling of that fact when she published a paper arguing that states should end the “master’s bump.” The money going toward degree-based pay raises—nearly $15 billion nationwide in the 2007–08 school year—was a waste, she argued. She authored that paper from her perch at the time at the University of Washington’s College of Education—the very sort of institution that was benefitting from the arrangement.

The North Carolina General Assembly eliminated master’s pay for newly hired teachers starting in the 2014-15 school year.  It remains the only state to eliminate salary supplements for master’s degrees.