The key is to get the scabs to heal and prevent new ones from forming so there's nothing to pick at. You might want to go to the doctor, because a prescription shampoo or solution might help. I used to have that same problem (including the other kids making fun). I use head and shoulders daily, and haven't had any problems in a while.
Maybe take something to fidget with in class instead of picking? A stress ball or something like that is unobtrusive and would give you something else to do with your hands.