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.