People to People International has been around foe about 45 years, and has a history of organizing trips and hosting international visitors. Their main website is at
http://www.ptpi.org/
None of my kids have participated in either their sports or other educational programs but my older (8th grade) daughter received an invitation to participate in what looked like a wonderful (but pricey) trip to Washington D.C. to visit and study U.S. government and historic sites, and both she and her sister have been invited to participate in the Sports Ambassadors program. Their web site is www.sportsambassadors.org
While I am sure that the soccer experience is totally legitimate, I think the real emphasis for the kids who participate is probably on the international travel experience.
An alternative for a kid who is really serious about the soccer might be to hook up as a guest player with a local team from your area that is travelling to Europe. In the KC area one or two of the most competitive teams from the U15, 16 or 17 age groups travel overseas most years. I suspect that's true elsewhere, and that there are occasionally spaces available because not all the regular players can make the trip
