See it's because I have a under cut that isn't allowed at school so I need an excuse
Answers (2)
You don't say anything that indicates any answer, so I have to guess. I guess you are seeing a doctor and are scheduled for some medical treatment. That is the reason. In general, it might be because they don't want your hair in their way, or they don't want your scummy hair getting into an open incision.
The only things I know that you would need to shave your head for is unremitting head lice and/or brain surgery. It's generally not done that I know of for any skin condition but there are some things like ringworm in which you might lose hair on the scalp but it wouldn't look as styled as an undercut.
May I suggest the democratic petition approach? If you can get enough parents to sign a petition to permit a more liberal range of haircuts, that might do more good. :)