Typically, one registers and insurers their vehicle in the state of which they are a resident, thus PA. In North Carolina you are considered a non-resident if you are an out of state college student who intends to return to your home state upon completion of your educations in NC.

That being said before registering the car in the home state of Pennsylvania your son should check to make sure an insurance policy bought in PA would fully cover him for his time in NC. Pennsylvania and North Carolina have different insurance requirements so he will want to make sure his PA insurance will cover any accidents he might have in NC or see if he needs to move his limits up to match NC's insurance requirements.

PA mandatory liability insurance limits are 15/30/5 while NC requires 30/60/25. Your son will want to make sure he is not under insured in the state in which he will be doing most of his driving. For what his college might suggest for a student in his situation, your son can speak with his university's student affairs office.

For more information regarding registering a car you can check with PennDOT or NC Division of Motor Vehicles, depending on what state it is determined he should register the vehicle in.