Perhaps this headline seems self-evident, but the backlash against licensure tests suggests otherwise. Those who still believe the common-sense maxim that, "you can't teach what you don't know" will be heartened but not surprised by new research from IES's Regional Educational Laboratory. Others can just be surprised.

Turns out that the teacher characteristics that most strongly predicted middle schoolers' grasp of algebra was their teachers' score on the state's most frequently taken licensure exam in mathematics—even more than their years of experience.

The predictive power of teachers' performance on math licensure exams held true across all kinds of kids, including students of color, those eligible for free or reduced price lunch, and notably students receiving special education services.

What generally didn't matter? Whether teachers were also certified to teach high school or had earned either or master's or doctorate.