by the time your in year 12 many of us adults you should able to decide what you do in your exam the school shouldn't be stopping anyone from leaving due to the fact that I think if we are old enough to drive and some of us to drink then we should be able to decide what is best for us in an exam situation so if leaving is what you want to do then you should be able to leave it's our HSC and if we choose to stuff it up by leaving too early then we should be old enough too handle the consequences.
i stayed for the whole time!! i needed it to think what the hell i could write for the crappy questions!!
but generally, at my school you cant leave during the first hour or the last 15 mins, but otherwise its all sweet.
all except one person stayed the whole time at my school!