1. Uni and Facebook. Not that it is too surprising!

2. Still! Researchers now nicely showed.
Skiera, Bernd / Hinz, Oliver / Spann, Martin (2015), "Social Media and Academic Performance: Does Facebook Activity Relate to Good Grades?", Schmalenbach Business Review, Vol. 67, Issue 1, 54-72

3. Here are the „hard facts“
Facebook Usage during class correlate negative with academic performance
Note that in Germany higher values for grade indicate a lower performance.
Skiera, Bernd / Hinz, Oliver / Spann, Martin (2015), "Social Media and Academic Performance: Does Facebook Activity Relate to Good Grades?", Schmalenbach Business Review, Vol. 67, Issue 1,
Source of picture:

4. What should you learn?. Use Facebook, but not during classes!