Should I have a Facebook account?

My class teacher is on Facebook and she has a Facebook account for our class to join the group. My teacher would post our homework into Facebook everyday. It is also a place where parents is able to post any queries or comments to her. Sometimes she would also post some comments e.g. what we like to eat.

I know how to login to Facebook. I have been logging into Facebook everyday using my Mami's account, most of the time to play a game called Backyard Monster. Because of school, I am only able to access into Facebook for a little while just to check on my pet Monster. I also know how to post new comments and read the comments posted by others. I have posted comments to my teachers before.

I was just asking Mami if I could open a Facebook account on my own. Obviously Mami said no and she felt that it was unnecessary at this present moment. I wonder when would be the appropriate time to do so.