Can schools penalize you for something that's not in the handbook?

I'm in a high school summer program and some boys snuck over to our hallway. I let a boy take my phone from me to call to get back to their hall. I have been kicked out of the program for allowing him to take my phone. This is NOT fair. There are no rules in the handbook stating cell phone borrowing is illegal. Can they penalize me for something that's not in the handbook? Any sites for help with my case would be appreciated as well. Thanks.