School districts likely will mislabel teachers as “effective” or “unsatisfactory,” teacher advocates say, if school officials rely on the state’s newly released teacher value-added scores, which measure a teacher’s impact on student learning.
The scores, which extend to many digits beyond a decimal point, aren’t as precise as they look. They come with an important caveat called the standard error. 
It is a statistical way to measure how stable or variable a set of numbers is, to help people decide how certain they can be of the numbers.
Up to 73 percent of the state’s teacher value-added scores, or VAM scores, have high standard errors, and up to a half may be high enough to make their scores possibly too close to call, experts said.
That means a teacher who is viewed as above average or below average may be average after all.
“These standard errors are so large that … it would be unfair to sort teachers into categories based on these numbers,” said Donna Mohr, a statistics professor at the University of North Florida who specializes in growth curves and