Girls make better grades because they're nicer?

Article here. Excerpt:

'Elementary and middle school teachers give higher grades to girls than boys — but that may be more about differences in behavior than differences in what they know, according to new research by University of Georgia economists.

“It appears that teachers see girls’ performance more favorably than boys’ performance,” said Christopher Cornwell, head of the UGA economics department and the study’s lead author.
...
“You would think there would be a close alignment between teachers’ assessment of performance and test scores, but they’re not as closely aligned as you’d think,” Cornwell said.

And that misalignment favors girls, he said.

“It’s not just that they’re not aligned. Boys are less favorably rendered than the girls,” he said.'