Okay. This is something a lot of people get confused about. There is a big difference between an Academy and an affiliate. Sporting KC has about a gazillion affiliates in the area, basically every major city/town and into Oklahoma and Nebraska even have SKC affiliates. Those are definitely not free and are probably expensive.
The Academy that has U-12s, U-17s and so on that plays and practices at the Swope Park facility is very selective and is a part of the club. For all intensive purposes, the kids on those squads are Pros, they go to their normal schools but then play for the club every day. Sporting has 17 year old Erik Palmer-Brown starting on the back line tonight that is a product of the academy.
It wouldn't surprise me if the Revs charge, that franchise is so f-ed up right now the league should get Kraft to sell it and move it to a better place
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Check out this article. MLS Academies are free of charge, but players don't receive financial compensation in order to retain NCAA eligibility.
http://espn.go.com/sports/soccer/news/_/id/6520002/mls-academies-kill-college-game-soccer