First I would really try and understand why what you did was wrong rather than just saying I didn’t so it. The school is probably much more apt to work with you if they see that your accepting responsibility for your part and working on earning their respect. Do your best and perhaps by 12th grade they will be willing to see that even though in 9th grade you knew what you were doing was wrong you worked hard to change and grow. However if your argument is that in 9th grade you didn’t know you were wrong I don’t think that will be helpful and they will be more apt to follow the policies and procedures.