It will depend upon the school, and to a lesser extent, the age of the student.
I will say that at any school that says no cars for boarders (which is most, if not all), there is no deviation from the rules. I would also say that most schools will give little to no leeway on the rules related to student safety (what cars they can ride in, when they can be off campus, modes of transportation into town, etc.) So you break the rule, you deal with the disciplinary action. For smaller offenses like dress code violation, the student might slide once or twice, but continued violation will certainly be dealt with.