We went in June and our ds (9) was picked. It was the highlight of our visit! I agree that you have to get in front and look enthusiastic! They select MANY children (at least 20), so if you don't get selected for the first show, come back again. The shows are about an hour apart. Ds wasn't selected for the first show, so we went to see the Muppet show, came back, and he was picked for the next show. If your son is a Star Wars fan, it's well worth it. They give the children an action figure and a Jedi training diploma when they're finished.
The "host" of the show did a great job. They had a couple boys who started to cry when Darth Vader approached them and he handled it very well.