Teacher quality is a leading factor affecting student achievement. Defining teacher quality, however, can be tricky—even trickier when comparing teachers worldwide.

 A new report published by the National Bureau of Economic Research (NBER) uses an international assessment of teachers' cognitive skills to examine gaps in student performance across the globe. As the National Center for Policy Analysis (NCPA) explains:

According to the report from [authors  Eric Hanushek of the Hoover Institution and Marc Piopiunik and Simon Wiederhold of the Institute for Economic Research] teachers' cognitive skills do have a significant relationship to student achievement:

Students in countries that score well on international achievement tests have teachers with higher numeracy and literacy skills.

Finland has the most skilled teachers according to PIAAC [the Programme for the International Assessment of Adult Competencies]. Were all countries to bring its teachers to the level of Finnish teachers, student performance would improve. The United States would see an increase in math performance of 54 percent of a standard deviation, while Russia would see math improvement of 73 percent of a standard deviation.

The authors also report that teachers' wages are related to teachers' cognitive skills; an increase in teacher salaries by one standard deviation is associated with an increase in teacher math skills of 40 percent of a standard deviation and an increase in literacy skills of 30 percent of a standard deviation.

Since one-quarter of a standard deviation is roughly the equivalent of one academic year’s (or grade level’s) worth of learning, American teachers with higher levels of cognitive skills could increase students’ math learning by more than two years and be compensated better for their superior performance. This report adds to mouting evidence that teacher training programs in the United States need to be more selective, graduation requirements should be more rigorous, and the teaching profession as a whole needs to be far more competitive to attract and keep the best and the brightest.