Is the Goal Better Teachers or Better Paid Teachers?

 From a study of incentives on teaching skills in North Carolina at the National Bureau of Economic Research:

Graduate degrees 

One of the most counterintuitive findings to emerge from the basic models is the small or negative effects of having a graduate degree. Most of those degrees are master’s degrees that generate higher salaries for teachers. A negative coefficient would suggest that having such a degree is not associated with higher achievement.  Thus, if the goal of the salary structure were to provide incentives for teachers to improve their teaching, the higher pay for master’s degrees would appear to
be money that is not well spent, except to the extent that the option of getting a master’s degree keeps effective experienced teachers in the profession.