"I called his boss yesterday to give him a head's up and explained to him the opportunity and that he's going"
Big ... NO NO from a Human Resources/Personnel point of view ...
He is a young adult already Diana, and I am sure you want only the very best for him ... my son is 13 by the way ...
I live in Texas ... it sounds likea great opportunity for your son to explore the world and grow a lot, but it has to be something he really wants to do, as a parent you have the right to push him a little but not to the extend of calling his employer ...LOL! ... he seems to be a well manered boy and didn't not backlash at you for doing that ... I am not criticizing you okay, it is funny what we moms would do sometimes ...