Tip for leveling up summons:
Leveling up summons is easy, but time consuming. You gain an experience point for each drive bar depleted for the duriation of the summon. So, all you have to do is go to an area that is completely void of heartless (like the underworld entrance) and summon anything. Now flip the channel and watch something for say... 3 minutes and then go back to your game. If your drive bar is out then just enter and quit one of the Underdrome cups, and repeat. Doing this it took about 2 hours to get my summons at level 7.