Another study has come in this week showing that teachers with National Board certification also happen to be quite effective in the classroom. Longtime critics of the advanced certification may need to start turning the volume knob down, because this study, like Goldhaber and Anthony's last year, is generally sound.

The author, Linda Cavalluzzo, of the nonprofit CNA Corporation loses a bit of academic credibility with her thinly disguised bias towards the National Board, but she backs it up with strong data. Using a large data set from Miami-Dade County Public Schools, Cavalluzzo examines student achievement in 9th and 10th grade mathematics for teachers who hold National Board certification as well as those who applied but failed, along with a whole host of other teacher attributes.

Even controlling for factors that normally indicate teacher effectiveness, students make statistically significant gains having been assigned NPBTS teachers (an increase of 12 percent of a standard deviation.) Critics may still question the hefty bonuses that National Board teachers get for producing this gain, or question that the bonuses aren't better targeted?Florida teachers for example get a few thousand to defray the cost of applying but also a 10 to 20 percent salary increase for ten years?but the charge that the process doesn't successfully identify better teachers may be evaporating.