Probably not. If I remember correctly there is no correlation (and sometimes even negative) between unearned praise and performance.

A more likely explanation which is backed up by evidence is that generalized perception of a group by the teacher will yield grades accordingly, so the more research that shows girls being better at school will become a self-fulfilling prophecy. Teachers have to work hard to counter this bias (and many do).

There is also a possibility that there is some biological difference that makes certain teaching methods that just so happen to be favored by teachers at the moment are a tiny bit easier for one gender over others. However I would like to see some research before I subscribe to that, but remain open for the possibility meanwhile.

That all said, if there is a difference, but the effect size is small, then honestly: Does it matter?