My question involves a traffic citation from the state of: Iowa

I have two questions.
1. Am I legally obligated to pay a parking ticket that has been administered to me by my high school?
2. Is it legal for the school to be able to hold a students diploma from them until they pay fees that were all issued by the school and not an officer of the law?

My sister mentioned to me awhile ago that it was not legal for my high school to hold students diplomas because they haven't paid things such as a parking ticket because that parking ticket is not actually legal. We don't sign any papers saying that as a student we agree to any terms of parking, or understand any conditions of diploma with holding or anything like that - we literally do not sign anything or have any verbal contract. They just give you the parking pass after you register your car and that's that. All that they say for a student to be able to graduate is that they complete the required courses.

Are either of these legal.

(All I am asking is that exact question as to whether or not they are legal. Yes, I understand why people get parking tickets, and I understand the point of having someone take responsibility for fee's they may owe; so please don't reply to this if you're only going to tell me that I should pay my tickets and fee's because it teaches me something about life. All I want to know is what I asked.)