There are numerous Student Exchange Programs that are on-going throughout the year in the United States. The key is contacting a Student Exchange Representative (phone number should be available through your son's school) and getting on the list.
Homestead High School in Fort Wayne Indiana has numerous Exchange Students that attend High School here during the school year.
As for something aviation related, the only thing that I can think of is this years EAA Air Venture Air Show in Oshkosh Wisconsin. You might be able to contact the EAA and see if they know of a family that would take him in during the summer so that he could volunteer to work at the Air Show.
Mike