Sorry but you don't need to go through a single school get your Sport ticket or even Private ticket. In fact most people don't go anywhere near a school to get a sport or private tickets, that's just if you want to accelerate the process or just need that extra re-assurance. They simply rent a plane and hire a CFI, read some books, take a written then practical test, done deal. Typically after sport or private one will seek out a school for further ratings after that level. The AMA could only wish they could propose such a successfully running program to get new, not as rich and health restricted pilots either up, or back up, in the air.
The test that the Sport Pilot and the CFI have to take are FAA tests. Written and practical, it's FAA mandated. With a parkflier you can buy and fly without ever having heard of the AMA. Sorry STL, (not really) but your analogy isn't relevant. The FAA "gate" he's talking about is real. You can't get a SP certificate without ever having heard of the FAA.