Time and again research has failed to find evidence that earning a master's degree makes a teacher more effective (with rare exceptions). It's not for lack of trying. Looking at the impact of advanced degrees on teachers in North Carolina, Kevin Bastian (of the University of North Carolina at Chapel Hill) finds that an in-area graduate degree (for example, a master's degree in mathematics for a math teacher) makes middle and high school math teachers more effective; however, there is little to no effect for teachers in any other subjects or grade levels. More critically, Bastian's findings suggest that "out-of-area" graduate degrees (school administration, counseling, curriculum specialist, etc.) generally make teachers less effective.
Still, most school districts continue to pay more for higher levels of education. Among nearly 150 large school districts in NCTQ's Teacher Contract Database, 82 percent start teachers holding master's degrees with salaries that are at least $1000 higher.
A notable exception? Bastian's own state of NC, which stopped paying teachers for advanced degrees earned after 2014.