DD14 got that invitation for People to People for this summer (not the 5th and 6th grade program).  I think it's overpriced for what it is, but I don't think it is a "scam" like some other similar programs are. 
  Has he done a talent search?  That is how they find kids like yours a lot of the time.  I know that just today we got a letter offering a scholarship to a boarding school, and we get these nonstop.  Most of them say something like "Because of your incredible score on the Duke TIP talent search", etc, but some don't.  
  I think teachers can nominate for these programs as well, if he hasn't done a talent search.