With the lack of an actual posed question, you are leaving much to the interpretation of editors and answerors with this question, and might receive more applicable ideas with a more detailed prompt.
My thought is that you can simply lump "facebook" into the ever growing list of instantaneous Internet driven student distraction and argue that it is having a negative impact on homework completion, general adherence to grammatical rules, and inability to put any thought toward a search query. I find that students who are not active on any social media networks tend to spend less time on the computer in general, and more time reading books, thinking through homework assignments, and maintaining smaller numbers of more genuine relationships. Facebook has opened up an entire world of counting friends, social competition (through witty status updates, pictures, and interesting posts that have little more than entertainment value), lack of connection to the real world.
Overall, I think it mostly negatively affects student "outcomes" of any kind.
Another positive side of facebook is the extension of the classroom. When managed properly, teachers can use facebook to help their students. It can be a great way to remind students of a field trip, project due date, or other important information. It can also be an easy way for students to ask questions they might have missed in class.
Another negative point has to do with bullying. Once, students could escape bullies at home, but now the bullying often follows the student on social sites like facebook. A student who feels they cannot escape their tormentors is likely to perform poorly in school.
Facebook is a social network site which is commonly used by youths and students included. The use of facebook may have both positive and negative impact on the students performances in class.
Positively, the students may use the site to discuss academic issues which may be of benefit to their studies but this may be on the rare occassions.
Contrary to this many students use this network site to connect to new friends for chatting thus spending most of their time unproductively leading to low grades in their exams.
Students who solely use Facebook for socializing has high chances of failing. Social networks like facebook are addictive and once one is into it he/she may be traped and fail to release him/herself leading to poor perfomances in school, thus having poor students outcomes in classwork.