Every MLS club has an academy. The best ones (RSL, LA, Dallas, NY, even TFC for all their professional level faults) are producing players who regularly feature on youth national teams and full national teams.
On top of that, you have the agreements from last season between MLS and USL that allows MLS teams to loan out up to 5 of their youth players to USL squads. LA wasn't happy with that setup though, so they actually started their own USL team for youth players,
LA Galaxy II. New York Red Bulls are doing
the same thing starting next season.
As for the impact that's had, here are the rosters for the youth national teams called in to camp in the last month
U-20s:
http://www.soccerbyives.net/2014/04/...rs-dallas.html
8 MLS
4 College
2 Mexico (note that Moreno was poached from NYRB's academy)
2 unattached (Moore just left IMG Academy, Rubin is signing with FC Utrecht on July 1)
1 NASL
1 local club
1 Brazil
1 France
1 England
GOALKEEPERS (2) : Santiago Castano (New York Red Bulls; Union City, N.J.), Zack Steffen (Maryland; Downington, Pa.)
DEFENDERS (9): Jordan Allen (Real Salt Lake; Rochester, N.Y.), Michael Amick (UCLA; Sunnyvale, Calif.), Sullaiman Dainkeh (Maryland; Reston, Va.), Trevor Haberkorn (Furman; Roanoke, Texas), Matthew Miazga (New York Red Bulls; Clifton, N.J.), Shaquell Moore (Unattached; Powder Springs, Ga.), Erik Palmer-Brown (Sporting KC; Lee’s Summit, Mo.), John Requejo Jr. (Real So Cal; Carpinteria, Calif.), Jesus Vazquez (UANL Tigres; San Luis Obispo, Calif.)
MIDFIELDERS (5): Kellyn Acosta (FC Dallas; Plano, Texas), Marco Delgado (Chivas USA; Glendora, Calif.), Luis Felipe (Cruzeiro; Ouro Branco, Brazil), Romain Gall (FC Lorient; Herndon, Va.), Lynden Gooch (Sunderland; Santa Cruz, Calif.)
FORWARDS (5): Benji Lopez (Real Salt Lake; San Diego, Calif.), Amando Moreno (Club Tijuana; Morganville, N.J.), Zach Pfeffer (Philadelphia Union; Dresher, Pa.), Rubio Rubin (Unattached; Beaverton, Ore.), Ben Spencer (Indy Eleven; Albuquerque, N.M.)
U-18s:
http://www.soccerbyives.net/2014/04/...es-canada.html
16 MLS (including Orlando City here)
5 local clubs
2 USL
1 England
GOALKEEPERS (3): Christian Herrera (Real Salt Lake AZ; Las Cruces, N.M.), Jonathan Klinsmann (Irvine Strikers; Newport Beach, Calif.), JT Marcinkowski (San Jose Earthquakes; Alamo, Calif.)
DEFENDERS (8): David Chavez (De Anza Force; Redwood City, Calif.), Justen Glad (Real Salt Lake AZ; Tucson, Ariz.), Malcolm Jones (LA Galaxy; Chino Hills, Calif.), Quentin Pearson (Colorado Rapids; Longmont, Colo.), Pablo Pelaez (San Diego Surf; San Diego, Calif.), Mauricio Pineda (Chicago Fire; Bolingbrook, Ill.), Alex Ramos (LA Galaxy; Reseda, Calif.), Tommy Redding (Orlando City SC; Oviedo, Fla.)
MIDFIELDERS (9): Mukwelle Akale (Minnesota Thunder; Minneapolis, Minn.), Kyle Scott (Chelsea; Bristol, England), Collin Fernandez (Chicago Fire; Downers Grove, Ill.), Patrick Jean-Giles (D.C. United; Lorton, Va.), Cameron Lindley (Chicago Fire; Carmel, Ind.), Stephen Payne (Chicago Magic PSG; Birmingham, Ala.), Sebastian Saucedo (Real Salt Lake AZ; Casa Grande, Ariz.), Ben Swanson (Crew Soccer Academy; Grove City, Ohio), Jackson Yueill (Minnesota Thunder; Bloomington, Minn.)
FORWARDS (4): Coy Craft (FC Dallas; Frisco, Texas), Sebastian Elney (Boca United; Boca Raton, Fla.), Christian Lucatero (Houston Dynamo; Pasadena, Texas), Jorge Ruiz (LA Galaxy; Mission Hills, Calif.)