AAU has its goal of taking kids to their national competition. USAG has policies and rules that "trickle down" from the international community relative to international elite competition. For this reason, the expectations of the athletes are a bit higher in some cases than other organizations. The AAU has created a more "user friendly" format, allowing in some cases for higher scoring with less stringent parameters.
The club program will dictate the abilities of the gymnast more than will the competitive environment. It is quite possible for an AAU athlete to obtain a scholarship, if she has the skill level necessary for it.
