I deactivated my Facebook account around the start of Year 11, not because of VCE or anything, but because it just annoyed me all the time. I'd been wanting to deactivate earlier, but a lot of photos of my friends were taken by me and uploaded on my account and so I would feel guilty taking those away, but then one of my friends told me not to worry about that.
I never reactivated that account. Because I genuinely dislike Facebook, it was pretty easy (after an initial stage of mindlessly going to Facebook out of habit before remembering I'd deactivated). You'll find that your real friends will still make the effort to contact you/invite you to things/etc., and vice versa. There are also plenty of better methods of procrastination.
I only made a new account earlier this year when I decided to run for a committee position in a club/society at university.
During high school at least, when you'll see most of your friends everyday at school anyway, I don't really think Facebook is that essential.