Things have changed with the Jedi training. Everybody needs to sign up now, and that's done near the entrance to Autopia (and Superhero HQ). Get there early (depending on the day of the week), and you will see a board with a list of times for the show for the day. You line up, and then when you get to the cast member, they will take down your details and you can select the time you want if it is available. You then come back to the area about 15 minutes before the start of the show, the kids put on their robes and get photographed by the Disney photog. They are then taken to the stage, and the parents / guardians are allowed to the front to view the show. No more mess of having kids jump up and down and be disappointed when they are not picked.
Your kids will love it! We went on an average weekday in January, got there at about 11am, and got in to the show at around 12:30 (can't remember the exact time).