No, a child’s hair is not the parent’s prerogative. A school, like a business, has the authority, and the responsibility, to set grooming standards for both students and employees.
If your child had to sit next to another child whose parent rolled him in dog feces every day before sending him to school, that would just be the parent’s prerogative, right?
The problem in this case is that the rule was misapplied, even after being challenged, and the principal deserves all the grief that followed. And it sounds like it was a considerable amount. The first requirement for any principal should be a healthy respect for common sense. That would go a long way toward eliminating these inane events.
A PUBLIC SCHOOL is NOT a private business and has NO authority to override a parent's dress and hair decisions. Health standards can cover your feces red herring example.