Dave don't ground him yet
Pressure is most likely the culprit, ie steam if you had low fluid level or if the thermostat wouldn't open. Check the resivour coolant level and remove thermostat put it in a pot of boiling water see if it opens (was that pot real good after). Was the engine damaged? A few more miles will tell AND check: the oil see if it has and lightbrown looking cottage cheese, smell exhaust (after its turned off) see if you can smell antifreeze and check the spark on each cylinder if a sparkplug isn't firing you have a cracked head (be careful doing this so you don't shock your self).
Depending how long your son drove I doubt any real damage was done, the iron block and iron head will expand and contract at close to the same rate, which is not the case with an aluminum head. If he starts to over heat in the future pull of the road, wait for a tow ie probably you
However if its a real jam he can wait for the truck to cool down then remove the thermostat this will allow coolant to flow no matter what (given he has coolant) even if your pump is bad just don't drive a long ways.