1. They don't have the right to take away the property of the student.
2. I would just never go to detention and taking property away would cause a fast law-suit if it happens more than once.
By the way, how can you ban a student from the school property for a week? Don't students have the right of a public education in the USA? (I know in Germany they have the right of education)
I had my own problems as student when I was around middle school age in Germany because I didn't participate in a Ethics class where the grade didn't count for anything in Berlin (but I was quiet in the back of class) and my sister had her problems in middle school and high school in the USA.
Schools should never be allowed to take your rights away even if most try to do it.