Every popular technology is going to be blamed for every wrong in the world. If it's not video games, it's Facebook that's ruining students' performance in school, a lot of people would tell you.
But according to one
study (PDF), that's not really true. In fact, the study found little significant correlation between Facebook use and grades and, what's more, it wasn't able to determine any causality.
The study found that the average student spends 106 minutes a day on Facebook. Yes, "a day." But students that spend a lot more time than that, another 93 minutes per day, didn't really that much worse grades, their GPA dropped by just 0.12 points. This was true for each 93 minutes added.
The study found some other correlation between activities on Facebook and grades, for example, those that prefer to share links or check up on friends have a higher GPA. But, again, there is no causality.