An important lesson for your son is to get the name/names of the person/people interviewing him. Everyone likes to be called by their name so a "Thank you, Mr. Sutton, for taking the time to see me" will put him a level or 2 above a lot of other 17 year olds.
But in this circumstance, he can just call back and ask for the manager. He should explain that he was interviewed for XYZ job last Friday (or whenever) and was just calling back to check if a decision has been made because that is the place he really wants to work. DH's cousin has a very large landscaping company and hires quite a few summer students. The ones he hires are the ones who keep calling him back to see if he's made a decision, if he's hired yet and if he's still hiring. He jokes that he says to them "Okay, I'll give you the job just so you'll stop bugging me" but his real rationale is that the kids who take the time to check back with him week after week are the ones who REALLY want the job and will work hard to keep the job. So if you son worries that he'll be "bugging" them and they won't give him the job for that reason, he need not worry.