Do credentials matter for North Carolina’s teachers? According to a new study by Charles T. Clotfelter, Helen F. Ladd, Jacob L. Vigdor, the answer is yes.

The authors find that credentials matter most for math achievement in grades 3, 4, and 5. I doubt that their findings would hold up for middle and high school teachers, but I digress. These winning credentials include experience, form of licensure, and licensure test. Master’s degrees generally had a negative effect on student achievement. National Board Certification identified better teachers but did not appear to make them more effective.

I am not surprised that teachers with any of these credentials produced greater gains on state mathematics tests. I do think experience makes a difference when it comes to quality math instruction, but I am less convinced that licensure matters. After all, experience and licensure are closely related. Teachers with more experience typically have a regular license, and, in this case, licensure may simply coincide with experience.

I am concerned that Clotfelter, Ladd, and Vigdor grouped all licensure tests (PRAXIS tests) together. Teachers may take different PRAXIS tests to earn certification. Some PRAXIS tests may be better predictors of performance than others, but, in general, I have no problem with the idea that better teachers probably achieve higher scores on PRAXIS tests.

Smaller effects were found for reading achievement. This is where the study fizzles, because the authors fail to explain why there is a difference between math and reading. What gives?

And then there is this finding, buried on page 26 of the report:

For math achievement, we find quite consistent results across models, with male teachers generating less positive results than female teachers, and black teachers less positive results than white teachers. For reading, in contrast, no differences emerge in the effectiveness of black and white teachers in any of the models. Of most interest is the finding that when a student and a teacher are the same race, the effects on student achievement are positive…

Anyone who attempts to use this study to justify teacher credentialing will have to deal with this issue.