As a teacher, I see many parents that don't want to make their kids mad at them. They want to be friends with their kids. Many parents expect the schools to raise their kids for them, or to be a babysitting service for 9-10 months. I've seen students cuss their parents in front of school personnel many times.
The kids know that the schools can't do much to discipline them. The worst thing most schools can do is to put the student in in-school suspension. State law does not allow out of school susupension to hurt the student's grade. When a student is susupended, they are taken off the roll, and their absence does not count against them. They just get those days off.